Chapter 5. NeoMutt's MIME Support
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# Chapter 5. NeoMutt's MIME Support

Quite a bit of effort has been made to make NeoMutt the premier text-mode MIME MUA. Every effort has been made to provide the functionality that the discerning MIME user requires, and the conformance to the standards wherever possible. When configuring NeoMutt for MIME, there are two extra types of configuration files which NeoMutt uses. One is the `mime.types` file, which contains the mapping of file extensions to IANA MIME types. The other is the `mailcap` file, which specifies the external commands to use for handling specific MIME types.

## 1. Using MIME in NeoMutt

### 1.1. MIME Overview

MIME is short for “Multipurpose Internet Mail Extension” and describes mechanisms to internationalize and structure mail messages. Before the introduction of MIME, messages had a single text part and were limited to us-ascii header and content. With MIME, messages can have attachments (and even attachments which itself have attachments and thus form a tree structure), nearly arbitrary characters can be used for sender names, recipients and subjects.

Besides the handling of non-ascii characters in message headers, to NeoMutt the most important aspect of MIME are so-called MIME types. These are constructed using a major and minor type separated by a forward slash. These specify details about the content that follows. Based upon these, NeoMutt decides how to handle this part. The most popular major type is “`text`” with minor types for plain text, HTML and various other formats. Major types also exist for images, audio, video and of course general application data (e.g. to separate cryptographically signed data with a signature, send office documents, and in general arbitrary binary data). There's also the `multipart` major type which represents the root of a subtree of MIME parts. A list of supported MIME types can be found in Table 5.1, “Supported MIME types”.

MIME also defines a set of encoding schemes for transporting MIME content over the network: `7bit`, `8bit`, `quoted-printable`, `base64` and `binary`. There're some rules when to choose what for encoding headers and/or body (if needed), and NeoMutt will in general make a good choice.

NeoMutt does most of MIME encoding/decoding behind the scenes to form messages conforming to MIME on the sending side. On reception, it can be flexibly configured as to how what MIME structure is displayed (and if it's displayed): these decisions are based on the content's MIME type. There are three areas/menus in dealing with MIME: the pager (while viewing a message), the attachment menu and the compose menu.

### 1.2. Viewing MIME Messages in the Pager

When you select a message from the index and view it in the pager, NeoMutt decodes as much of a message as possible to a text representation. NeoMutt internally supports a number of MIME types, including the `text/plain` type, the `message/rfc822` (mail messages) type and some `multipart` types. In addition, it recognizes a variety of PGP MIME and S/MIME types, including PGP/MIME and `application/pgp`, and `application/pkcs7-mime`.

NeoMutt will denote attachments with a couple lines describing them. These lines are of the form:

    [-- Attachment #1: Description --]
    [-- Type: text/plain, Encoding: 7bit, Size: 10000 --]

Where the Description is the description or filename given for the attachment, and the Encoding is one of the already mentioned content encodings.

If NeoMutt cannot deal with a MIME type, it will display a message like:

    [-- image/gif is unsupported (use 'v' to view this part) --]

### 1.3. The Attachment Menu

The default binding for `<view-attachments>` is “v”, which displays the attachment menu for a message. The attachment menu displays a list of the attachments in a message. From the attachment menu, you can save, print, pipe, delete, and view attachments. You can apply these operations to a group of attachments at once, by tagging the attachments and by using the `<tag-prefix>` operator. You can also reply to the current message from this menu, and only the current attachment (or the attachments tagged) will be quoted in your reply. You can view attachments as text, or view them using the mailcap viewer definition (the mailcap mechanism is explained later in detail).

Finally, you can apply the usual message-related functions (like `<resend-message>`, and the `<reply>` and `<forward>` functions) to attachments of type `message/rfc822`.

See table Table 9.7, “Default Attachment Menu Bindings” for all available functions.

#### 1.3.1. Viewing Attachments

There are four(!) ways of viewing attachments, so the functions deserve some extra explanation.

`<view-mailcap>` (default keybinding: m)

  This will use the first matching mailcap entry.

  If no matching mailcap entries are found, it will abort with an error message.

`<view-attach>` (default keybinding: <Enter>)

  NeoMutt will display internally supported MIME types (see Section 1.2, “Viewing MIME Messages in the Pager”) in the pager. This will respect auto_view settings, to determine whether to use a `copiousoutput` mailcap entry or just directly display the attachment.

  Other MIME types will use the first matching mailcap entry.

  If no matching mailcap entries are found, the attachment will be displayed in the pager as raw text.

`<view-pager>`

  NeoMutt will use the first matching `copiousoutput` mailcap entry to display the attachment in the pager (regardless of auto_view settings).

  If no matching mailcap entries are found, the attachment will be displayed in the pager as raw text.

`<view-text>` (default keybinding: T)

  The attachment will always be displayed in the pager as raw text.

### 1.4. The Compose Menu

The compose menu is the menu you see before you send a message. It allows you to edit the recipient list, the subject, and other aspects of your message. It also contains a list of the attachments of your message, including the main body. From this menu, you can print, copy, filter, pipe, edit, compose, review, and rename an attachment or a list of tagged attachments. You can also modifying the attachment information, notably the type, encoding and description.

Attachments appear as follows by default:

    - 1 [text/plain, 7bit, 1K]           /tmp/neomutt-euler-8082-0 <no description>
      2 [applica/x-gunzip, base64, 422K] ~/src/neomutt-0.85.tar.gz <no description>

The “-” denotes that NeoMutt will delete the file after sending (or postponing, or canceling) the message. It can be toggled with the `<toggle-unlink>` command (default: u). The next field is the MIME content-type, and can be changed with the `<edit-type>` command (default: ^T). The next field is the encoding for the attachment, which allows a binary message to be encoded for transmission on 7bit links. It can be changed with the `<edit-encoding>` command (default: ^E). The next field is the size of the attachment, rounded to kilobytes or megabytes. The next field is the filename, which can be changed with the `<rename-file>` command (default: R). The final field is the description of the attachment, and can be changed with the `<edit-description>` command (default: d). See $attach_format for a full list of available expandos to format this display to your needs.

## 2. MIME Type Configuration with `mime.types`

To get most out of MIME, it's important that a MIME part's content type matches the content as closely as possible so that the recipient's client can automatically select the right viewer for the content. However, there's no reliable way for NeoMutt to know how to detect every possible file type. Instead, it uses a simple plain text mapping file that specifies what file extension corresponds to what MIME type. This file is called `mime.types`.

When you add an attachment to your mail message, NeoMutt searches the system `mime.types` file at `/etc/mime.types`, `$SYSCONFDIR/mime.types` or `$PKGDATADIR/mime.types` and then your personal `mime.types` file at `$HOME/.mime.types`.

Where `$HOME` is your home directory. The `$PKGDATADIR` and the `$SYSCONFDIR` directories depend on where NeoMutt is installed: the former is the default for shared data, the latter for system configuration files.

Each line starts with the full MIME type, followed by a space and space-separated list of file extensions. For example you could use:

Example 5.1. `mime.types`

    application/postscript          ps eps
    application/pgp                 pgp
    audio/x-aiff                    aif aifc aiff

A sample `mime.types` file comes with the NeoMutt distribution, and should contain most of the MIME types you are likely to use.

If NeoMutt can not determine the MIME type by the extension of the file you attach, it will run the command specified in $mime_type_query_command. If that command is not specified, NeoMutt will look at the file. If the file is free of binary information, NeoMutt will assume that the file is plain text, and mark it as `text/plain`. If the file contains binary information, then NeoMutt will mark it as `application/octet-stream`. You can change the MIME type that NeoMutt assigns to an attachment by using the `<edit-type>` command from the compose menu (default: ^T), see Table 5.1, “Supported MIME types” for supported major types. NeoMutt recognizes all of these if the appropriate entry is found in the `mime.types` file. Non-recognized mime types should only be used if the recipient of the message is likely to be expecting such attachments.

Table 5.1. Supported MIME types

MIME major type | Standard | Description
--- | --- | ---
`application` | yes | General application data
`audio` | yes | Audio data
`image` | yes | Image data
`message` | yes | Mail messages, message status information
`model` | yes | VRML and other modeling data
`multipart` | yes | Container for other MIME parts
`text` | yes | Text data
`video` | yes | Video data
`chemical` | no | Mostly molecular data

MIME types are not arbitrary, they need to be assigned by IANA.

## 3. MIME Viewer Configuration with Mailcap

NeoMutt supports RFC1524 MIME Configuration, in particular the Unix specific format specified in Appendix A of RFC1524. This file format is commonly referred to as the “mailcap” format. Many MIME compliant programs utilize the mailcap format, allowing you to specify handling for all MIME types in one place for all programs. Programs known to use this format include Firefox, lynx and metamail.

In order to handle various MIME types that NeoMutt doesn't have built-in support for, it parses a series of external configuration files to find an external handler. The default search string for these files is a colon delimited list containing the following files:

1. `$HOME/.mailcap`

2. `$PKGDATADIR/mailcap`

3. `$SYSCONFDIR/mailcap`

4. `/etc/mailcap`

5. `/usr/etc/mailcap`

6. `/usr/local/etc/mailcap`

where `$HOME` is your home directory. The `$PKGDATADIR` and the `$SYSCONFDIR` directories depend on where NeoMutt is installed: the former is the default for shared data, the latter for system configuration files.

The default search path can be obtained by running the following command:

    neomutt -nF /dev/null -Q mailcap_path

In particular, the metamail distribution will install a mailcap file, usually as `/usr/local/etc/mailcap`, which contains some baseline entries.

### 3.1. The Basics of the Mailcap File

A mailcap file consists of a series of lines which are comments, blank, or definitions.

A comment line consists of a # character followed by anything you want.

A blank line is blank.

A definition line consists of a content type, a view command, and any number of optional fields. Each field of a definition line is divided by a semicolon “;” character.

The content type is specified in the MIME standard “type/subtype” notation. For example, `text/plain`, `text/html`, `image/gif`, etc. In addition, the mailcap format includes two formats for wildcards, one using the special “*” subtype, the other is the implicit wild, where you only include the major type. For example, `image/*`, or `video` will match all image types and video types, respectively.

The view command is a Unix command for viewing the type specified. There are two different types of commands supported. The default is to send the body of the MIME message to the command on stdin. You can change this behavior by using `%s` as a parameter to your view command. This will cause NeoMutt to save the body of the MIME message to a temporary file, and then call the view command with the `%s` replaced by the name of the temporary file. In both cases, NeoMutt will turn over the terminal to the view program until the program quits, at which time NeoMutt will remove the temporary file if it exists. This means that mailcap does not work out of the box with programs which detach themselves from the terminal right after starting, like `open` on Mac OS X. In order to nevertheless use these programs with mailcap, you probably need custom shell scripts.

So, in the simplest form, you can send a `text/plain` message to the external pager more on standard input:

    text/plain; more

Or, you could send the message as a file:

    text/plain; more %s

Perhaps you would like to use lynx to interactively view a `text/html` message:

    text/html; lynx %s

In this case, lynx does not support viewing a file from standard input, so you must use the `%s` syntax.

### Note

Some older versions of lynx contain a bug where they will check the mailcap file for a viewer for `text/html`. They will find the line which calls lynx, and run it. This causes lynx to continuously spawn itself to view the object.

On the other hand, maybe you don't want to use lynx interactively, you just want to have it convert the `text/html` to `text/plain`, then you can use:

    text/html; lynx -dump %s | more

Perhaps you wish to use lynx to view `text/html` files, and a pager on all other text formats, then you would use the following:

    text/html; lynx %s
    text/*; more

### 3.2. Secure Use of Mailcap

The interpretation of shell meta-characters embedded in MIME parameters can lead to security problems in general. NeoMutt tries to quote parameters in expansion of `%s` syntaxes properly, and avoids risky characters by substituting them, see the $mailcap_sanitize variable.

Although NeoMutt's procedures to invoke programs with mailcap seem to be safe, there are other applications parsing mailcap, maybe taking less care of it. Therefore you should pay attention to the following rules:

Keep the %-expandos away from shell quoting. Don't quote them with single or double quotes. NeoMutt does this for you, the right way, as should any other program which interprets mailcap. Don't put them into backtick expansions. Be highly careful with eval statements, and avoid them if possible at all. Trying to fix broken behavior with quotes introduces new leaks – there is no alternative to correct quoting in the first place.

If you have to use the %-expandos' values in context where you need quoting or backtick expansions, put that value into a shell variable and reference the shell variable where necessary, as in the following example (using `$charset` inside the backtick expansion is safe, since it is not itself subject to any further expansion):

    text/test-mailcap-bug; cat %s; copiousoutput; test=charset=%{charset} \
            && test "`echo $charset | tr '[A-Z]' '[a-z]'`" != iso-8859-1

### 3.3. Advanced Mailcap Usage

#### 3.3.1. Optional Fields

In addition to the required content-type and view command fields, you can add semi-colon “;” separated fields to set flags and other options. NeoMutt recognizes the following optional fields:

copiousoutput

  This flag tells NeoMutt that the command passes possibly large amounts of text on standard output. This causes NeoMutt to invoke a pager (either the internal pager or the external pager defined by the pager variable) on the output of the view command. Without this flag, NeoMutt assumes that the command is interactive. One could use this to replace the pipe to `more` in the `lynx -dump` example in the Basic section:

      text/html; lynx -dump %s ; copiousoutput

  This will cause lynx to format the `text/html` output as `text/plain` and NeoMutt will use your standard pager to display the results.

  NeoMutt will set the `COLUMNS` environment variable to the width of the pager. Some programs make use of this environment variable automatically. Others provide a command line argument that can use this to set the output width:

      text/html; lynx -dump -width ${COLUMNS:-80} %s; copiousoutput

  Note that when using the built-in pager, only entries with this flag will be considered a handler for a MIME type – all other entries will be ignored.

needsterminal

  NeoMutt uses this flag when viewing attachments with auto_view, in order to decide whether it should honor the setting of the $wait_key variable or not. When an attachment is viewed using an interactive program, and the corresponding mailcap entry has a needsterminal flag, NeoMutt will use $wait_key and the exit status of the program to decide if it will ask you to press a key after the external program has exited. In all other situations it will not prompt you for a key.

compose=<command>

  This flag specifies the command to use to create a new attachment of a specific MIME type. NeoMutt supports this from the compose menu.

composetyped=<command>

  This flag specifies the command to use to create a new attachment of a specific MIME type. This command differs from the compose command in that NeoMutt will expect standard MIME headers on the data. This can be used to specify parameters, filename, description, etc. for a new attachment. NeoMutt supports this from the compose menu.

print=<command>

  This flag specifies the command to use to print a specific MIME type. NeoMutt supports this from the attachment and compose menus.

edit=<command>

  This flag specifies the command to use to edit a specific MIME type. NeoMutt supports this from the compose menu, and also uses it to compose new attachments. NeoMutt will default to the defined $editor for text attachments.

nametemplate=<template>

  This field specifies the format for the file denoted by `%s` in the command fields. Certain programs will require a certain file extension, for instance, to correctly view a file. For instance, lynx will only interpret a file as `text/html` if the file ends in `.html`. So, you would specify lynx as a `text/html` viewer with a line in the mailcap file like:

      text/html; lynx %s; nametemplate=%s.html

test=<command>

  This field specifies a command to run to test whether this mailcap entry should be used. The command is defined with the command expansion rules defined in the next section. If the command returns 0, then the test passed, and NeoMutt uses this entry. If the command returns non-zero, then the test failed, and NeoMutt continues searching for the right entry. Note that the content-type must match before NeoMutt performs the test. For example:

      text/html; firefox -remote 'openURL(%s)' ; test=RunningX
      text/html; lynx %s

  In this example, NeoMutt will run the program `RunningX` which will return 0 if the X Window manager is running, and non-zero if it isn't. If `RunningX` returns 0, then NeoMutt will run firefox to display the `text/html` object. If RunningX doesn't return 0, then NeoMutt will go on to the next entry and use lynx to display the `text/html` object.

x-neomutt-keep

  `x-neomutt-keep` tells NeoMutt to not delete the temporary file after the program has been run.

  Using it allows you to control the lifespan of the temporary file. Without this option, the file will be deleted after $timeout seconds.

      text/html; firefox %s & x-neomutt-keep

x-neomutt-nowrap

  `x-neomutt-nowrap` tells the NeoMutt pager to ignore the $wrap parameter and to assume the output from the mailcap command to already be correctly wrapped.

      text/html; /usr/local/bin/w3m -s -T text/html -o display_link_number=1 %s; nametemplate=%s.html; copiousoutput; x-neomutt-nowrap;

#### 3.3.2. Search Order

When searching for an entry in the mailcap file, NeoMutt will search for the most useful entry for its purpose. For instance, if you are attempting to print an `image/gif`, and you have the following entries in your mailcap file, NeoMutt will search for an entry with the print command:

    image/*;        xv %s
    image/gif;      ; print=anytopnm %s | pnmtops | lpr; \
                    nametemplate=%s.gif

NeoMutt will skip the `image/*` entry and use the `image/gif` entry with the print command.

In addition, you can use this with auto_view to denote two commands for viewing an attachment, one to be viewed automatically, the other to be viewed interactively from the attachment menu using the `<view-mailcap>` function (bound to “m” by default). In addition, you can then use the test feature to determine which viewer to use interactively depending on your environment.

    text/html;      firefox -remote 'openURL(%s)' ; test=RunningX
    text/html;      lynx %s; nametemplate=%s.html
    text/html;      lynx -dump %s; nametemplate=%s.html; copiousoutput

For auto_view, NeoMutt will choose the third entry because of the `copiousoutput` tag. For interactive viewing, NeoMutt will run the program `RunningX` to determine if it should use the first entry. If the program returns non-zero, NeoMutt will use the second entry for interactive viewing. The last entry is for inline display in the pager and the `<view-attach>` function in the attachment menu.

Entries with the `copiousoutput` tag should always be specified as the last one per type. For non-interactive use, the last entry will then actually be the first matching one with the tag set. For non-interactive use, only `copiousoutput`-tagged entries are considered. For interactive use, NeoMutt ignores this tag and treats all entries equally. Therefore, if not specified last, all following entries without this tag would never be considered for `<view-attach>` because the `copiousoutput` before them matched already.

#### 3.3.3. Command Expansion

The various commands defined in the mailcap files are passed to the `/bin/sh` shell using the `system(3)` function. Before the command is passed to `/bin/sh -c`, it is parsed to expand various special parameters with information from NeoMutt. The keywords NeoMutt expands are:

%s

  As seen in the basic mailcap section, this variable is expanded to a filename specified by the calling program. This file contains the body of the message to view/print/edit or where the composing program should place the results of composition. In addition, the use of this keyword causes NeoMutt to not pass the body of the message to the view/print/edit program on stdin.

%t

  NeoMutt will expand `%t` to the text representation of the content type of the message in the same form as the first parameter of the mailcap definition line, i.e. `text/html` or `image/gif`.

%{<parameter>}

  NeoMutt will expand this to the value of the specified parameter from the Content-Type: line of the mail message. For instance, if your mail message contains:

      Content-Type: text/plain; charset=iso-8859-1

  then NeoMutt will expand `%{charset}` to “iso-8859-1”. The default metamail mailcap file uses this feature to test the charset to spawn an xterm using the right charset to view the message.

\%

  This will be replaced by a literal `%`.

NeoMutt does not currently support the `%F` and `%n` keywords specified in RFC1524. The main purpose of these parameters is for multipart messages, which is handled internally by NeoMutt.

### 3.4. Example Mailcap Files

This mailcap file is fairly simple and standard:

    # I'm always running X :)
    video/*;        xanim %s > /dev/null
    image/*;        xv %s > /dev/null
    # I'm always running firefox (if my computer had more memory, maybe)
    text/html;      firefox -remote 'openURL(%s)'

These mailcap files shows how to control the lifespan of the temporary file.

    # The `display` program shows an image and doesn't return until the user quits.

    # Display an image, but wait for the user to quit the display program.
    # When the user quits control will return to NeoMutt.
    image/png; display %s;

    # Display an image and return to NeoMutt immediately.
    image/png; display %s &;

    # The file will be automatically deleted after $timeout seconds.

    # Some graphical programs return immediately if they're already running.
    # We'll add an ampersand (&), just in case they're not.

    # View the contents of a 'tar' file.
    # The file will be automatically deleted after $timeout seconds.
    application/x-tar; file-roller %s &;

    # View the contents of a 'tar' file.
    # The file will not be deleted.
    application/x-tar; file-roller %s &; x-neomutt-keep

    # Some programs watch any files they have open.
    # If NeoMutt deleted the file, the program would close prematurely.

    # Use a custom script to manage the file's lifespan.
    application/pdf; my-pdf-script.sh %s; x-neomutt-keep

This mailcap file shows quite a number of examples:

    # Use xanim to view all videos Xanim produces a header on startup,
    # send that to /dev/null so I don't see it
    video/*;        xanim %s > /dev/null
    # Send html to a running firefox by remote
    text/html;      firefox -remote 'openURL(%s)'; test=RunningFirefox
    # If I'm not running firefox but I am running X, start firefox on the
    # object
    text/html;      firefox %s; test=RunningX
    # Else use lynx to view it as text
    text/html;      lynx %s
    # This version would convert the text/html to text/plain
    text/html;      lynx -dump %s; copiousoutput
    # I use enscript to print text in two columns to a page
    text/*;         more %s; print=enscript -2Gr %s
    # Firefox adds a flag to tell itself to view jpegs internally
    image/jpeg;     xv %s; x-mozilla-flags=internal
    # Use xv to view images if I'm running X
    # In addition, this uses the \ to extend the line and set my editor
    # for images
    image/*;        xv %s; test=RunningX; edit=xpaint %s
    # Convert images to text using the netpbm tools
    image/*;        (anytopnm %s | pnmscale -xysize 80 46 | ppmtopgm | pgmtopbm | \
                    pbmtoascii -1x2) 2>&1 ; copiousoutput
    # Send excel spreadsheets to my NT box
    application/ms-excel;   open.pl %s

## 4. MIME Autoview

Usage:

`auto_view` `mime-type` [ `/mime-subtype` ] [ `mime-type` [ `/mime-subtype` ] ...]
`unauto_view` { * | [ `mime-type` [ `/mime-subtype` ] ...]}

In addition to explicitly telling NeoMutt to view an attachment with the MIME viewer defined in the mailcap file from the attachments menu, NeoMutt has support for automatically viewing MIME attachments while in the pager.

For this to work, you must define a viewer in the mailcap file which uses the `copiousoutput` option to denote that it is non-interactive. Usually, you also use the entry to convert the attachment to a text representation which you can view in the pager.

You then use the auto_view configuration command to list the content-types that you wish to view automatically. For instance, if you set it to:

    auto_view text/html application/x-gunzip \
      application/postscript image/gif application/x-tar-gz

...NeoMutt would try to find corresponding entries for rendering attachments of these types as text. A corresponding mailcap could look like:

    text/html;              lynx -dump %s; copiousoutput; nametemplate=%s.html
    image/*;                anytopnm %s | pnmscale -xsize 80 -ysize 50 | ppmtopgm | \
                            pgmtopbm | pbmtoascii ; copiousoutput
    application/x-gunzip;   gzcat; copiousoutput
    application/x-tar-gz;   gunzip -c %s | tar -tf - ; copiousoutput
    application/postscript; ps2ascii %s; copiousoutput

unauto_view can be used to remove previous entries from the auto_view list. This can be used with message-hook to autoview messages based on size, etc. “unauto_view *” will remove all previous entries.

## 5. MIME Multipart/Alternative

A `multipart/alternative` email has several parts that represent the same content in different formats, such as `text/plain` and `text/html`. This kind of email is heavily used by many modern mail user agents to send HTML messages which contain an alternative plain text representation. You can read and write `multipart/alternative` emails in NeoMutt.

### 5.1. Reading Multipart/Alternative Emails

NeoMutt has some heuristics for determining which attachment of a `multipart/alternative` type to display:

1. First, NeoMutt will check the alternative_order list to determine if one of the available types is preferred. It consists of a number of MIME types in order, including support for implicit and explicit wildcards. For example:

       alternative_order text/enriched text/plain text application/postscript image/*

2. Next, NeoMutt will check if any of the types have a defined auto_view, and use that.

3. Failing that, NeoMutt will look first for `text/enriched`, followed by `text/plain`, and finally `text/html`.

4. As a last attempt, NeoMutt will look for any type it knows how to handle.

To remove a MIME type from the alternative_order list, use the unalternative_order command.

### 5.2. Composing Multipart/Alternative Emails

Noemutt includes some primitive ability to compose multipart/alternative emails:

1. In the Compose menu, attach the two (or more) alternatives as usual. For example, attach "invitation.html" and then "invitation.txt". (You can reorder them using the `<move-up>` (-) and `<move-down>` (+) bindings, and edit the descriptions).

2. Tag the attachments that are alternatives, and press the `<group-alternatives>` (&) binding to group them together. After this, the separate parts will be displayed in a tree structure. Attachments can still be edited separately and reordered within the group, but must be ungrouped using the `<ungroup-attachment>` (#) binding for more advanced editing before tagging and grouping together again as described above.

3. Send the email as usual.

If all the attachments have been grouped and form a single `multipart/alternative`, part then this message will be sent as a `multipart/alternative` email, otherwise it will be sent as a `multipart/mixed` email.

Be aware that when sending a `multipart/alternative` email, you have to manually prepare the alternative parts and attach them. However, you can use Neomutt's macro to perform all the operations needed, such that you can compose a plain text email as usual and turn that into a `multipart/alternative` email in one single command, with one part being `text/plain` and the other `text/html`. An example macro which adds an HTML part to the main body of an email and sends it could be the following:

    macro compose Y "<first-entry><enter-command>set wait_key=no<enter>\
    <pipe-entry>pandoc -o /tmp/neomutt-alternative.html<enter>\
    <attach-file>/tmp/neomutt-alternative.html<enter>\
    <toggle-unlink><toggle-disposition>\
    <tag-entry><first-entry><tag-entry><group-alternatives>\
    <enter-command>set wait_key=yes<enter><send-message>" \
    "send the message as 'multipart/alternative'"

## 6. MIME Multipart/Multilingual

Neomutt includes supports for reading and writing `multipart/multilingual` emails. A `multipart/multilingual` email is like a `multipart/alternative` email, except that it comes with parts of different versions of languages instead of appearances. Its format is described by RFC8255.

### 6.1. Reading Multipart/Multilingual Emails

Neomutt uses the `$preferred_languages` variable to determine which languages to display when displaying a `multipart/multilingual` email. You can have several preferred languages, separated by `,`

    set preferred_languages="fr,en,de"

Neomutt will try to match these strings again the multilingual header in the received emails "by prefix", e.g., `en` will match both `en` and `en_US`.

If `$preferred_languages` is not set, it default to None, and the first part of the received `multipart/multilingual` email will be displayed.

### 6.2. Composing Multipart/Multilingual Emails

The procedures of composing a `multipart/multilingual` email is similar to those in Composing Multipart/Alternative. You have to prepare every part manually or using some scripts, and then tag and group them together into a `multipart/multilingual` bundle before sending it:

1. Prepare parts of the multilingual emails.

2. Attach them as attachments.

3. Tag them with `<tag-entry>`

4. Edit the `Content-Language` header of every attachment with command `<edit-language>` (default to `Ctrl-L`). This is important, otherwise the recipient of this email will not know the corresponding languages. You can set arbitrary string as `Content-Language`, but it is recommended to set it as some common prefixes such as "en", "zh" and "fr".

5. Group all the tag messages together by `<group-multilingual>` (default to `^`).

6. Send the email as usual.

As in Composing Multipart/Alternative, you can also use Neomutt's macro and some external scripts to combine this procedure into one.

After grouping the separate parts will be displayed in a tree structure. Attachments can still be edited separately and reordered within the group, but must be ungrouped using the `<ungroup-attachment>` (#) binding for more advanced editing before tagging and grouping together again as described above.

## 7. MIME Multipart/Related

Neomutt doesn't include any special support for reading `multipart/related` emails, but it is possible to write a `multipart/related` email. A `multipart/related` attachment is intended for compound objects consisting of several inter-related body parts which are linked together using the `Content-ID` header. Its format is described by RFC2387.

### 7.1. Composing Multipart/Related Emails

The procedure for composing a `multipart/related` email is similar to that in Composing Multipart/Alternative. You have to prepare every part manually or using some scripts, and then tag and group them together into a `multipart/related` bundle before sending it:

1. Prepare parts of the related email.

2. Attach them as attachments.

3. Tag them with `<tag-entry>`

4. One part can reference another using its `Content-ID` header. For example, an HTML part that includes an embedded image needs to contain: `<img src="cid:content-id">` where an attached image has a `Content-ID` header of `content-id`. The `Content-ID` of an attachment can be set using `<edit-content-id>` (default key `Alt-i`). `<edit-content-id>` sets a random ID which can then be changed if desired. Permitted characters for `Content-ID` are: `-.0-9@A-Z_a-z`.

   If the `multipart/related` group is intended to be inline, members of the group should also have their `Content-Disposition` header set to `inline` which can be toggled using `<toggle-disposition>` (default key `Ctrl-D`).

   It can also be desirable to give referenced files in the group a `filename` even when the `Content-Disposition` is set to be `inline`. To do this use `<rename-attachment>` (default key `Ctrl-O`).

5. Group all the tagged messages together with `<group-related>` (default key `%`).

   Top level attachments (excluding `multipart` ones) in the group are automatically given a random `Content-ID` if they do not already have one.

6. Send the email as usual.

Some care needs to be taken with the construction of a `multipart/related` email to ensure it is correctly displayed by the receiving mail client. A typical email with a `multipart/alternative` part containing a `text/plain` part and a `text/html` part with an embedded image, along with a separate attachment might end up like this:

      I     1 <no description>                                         [multipart/related, 7bit, 0K]
      I     2 ├─><no description>                                  [multipart/alternative, 7bit, 0K]
    - I     3 │ ├─>/tmp/neomutt-hostname-XXXX-XXXXXX-XXXXXXXXXX   [text/plain, 7bit, us-ascii, 0.1K]
    - I     4 │ └─>/tmp/neomutt-alternative.html                      [text/html, 8bit, utf-8, 0.6K]
      I     5 └─>image.png                                                  [image/png, base64, 19K]
      A     6 attachment.pdf                                         [application/pdf, quoted, 7.1K]

In the above email `/tmp/neomutt-alternative.html` would reference `image.png` using `<img src="cid:content-id">` and `image.png` has been given an explicit name of `image.png` using `<rename-attachment>` (regardless of its initial filename). `<group-related>` has set its `Content-ID` header to a random value.

## 8. Attachment Searching and Counting

If you ever lose track of attachments in your mailboxes, NeoMutt's attachment-counting and -searching support might be for you. You can make your message index display the number of qualifying attachments in each message, or search for messages by attachment count. You also can configure what kinds of attachments qualify for this feature with the attachments and unattachments commands.

In order to provide this information, NeoMutt needs to fully MIME-parse all messages affected first. This can slow down operation especially for remote mail folders such as IMAP because all messages have to be downloaded first regardless whether the user really wants to view them or not though using Section 8.2, “Body Caching” usually means to download the message just once.

By default, NeoMutt will not search inside `multipart/alternative` containers. This can be changed via the $count_alternatives configuration variable.

The syntax is:

`attachments` { + | - } `disposition` `mime-type` [ `mime-type` ...]
`unattachments` { + | - } `disposition` `mime-type` [ `mime-type` ...]
`attachments` `?`
`unattachments` `*`

disposition is the attachment's Content-Disposition type – either `inline` or `attachment`. You can abbreviate this to `I` or `A`.

Disposition is prefixed by either a “+” symbol or a “-” symbol. If it's a “+”, you're saying that you want to allow this disposition and MIME type to qualify. If it's a “-”, you're saying that this disposition and MIME type is an exception to previous “+” rules. There are examples below of how this is useful.

mime-type is the MIME type of the attachment you want the command to affect. A MIME type is always of the format `major/minor`, where `major` describes the broad category of document you're looking at, and `minor` describes the specific type within that category. The major part of mime-type must be literal text (or the special token “`*`”), but the minor part may be a regular expression. (Therefore, “`*/.*`” matches any MIME type.)

The MIME types you give to the attachments directive are a kind of pattern. When you use the attachments directive, the patterns you specify are added to a list. When you use unattachments, the pattern is removed from the list. The patterns are not expanded and matched to specific MIME types at this time – they're just text in a list. They're only matched when actually evaluating a message.

Note that the first MIME part is treated slightly differently: It is almost always the message text. Thus, it is not counted as an attachment if its disposition is `inline` and it is not a `multipart/*` or `message/*` MIME-type.

Some examples might help to illustrate. The examples that are not commented out define the default configuration of the lists.

Example 5.2. Attachment counting

    # Removing a pattern from a list removes that pattern literally. It
    # does not remove any type matching the pattern.
    #
    #  attachments   +A */.*
    #  attachments   +A image/jpeg
    #  unattachments +A */.*
    #
    # This leaves "attached" image/jpeg files on the allowed attachments
    # list. It does not remove all items, as you might expect, because the
    # second */.* is not a matching expression at this time.
    #
    # Remember: "unattachments" only undoes what "attachments" has done!
    # It does not trigger any matching on actual messages.
    #
    # Qualify any MIME part with an "attachment" disposition, EXCEPT for
    # text/vcard, text/x-vcard, application/pgp.*, application/pkcs7-.* and
    # application/x-pkcs7-.* parts. (PGP and S/MIME parts are already known
    # to NeoMutt, and can be searched for with ~g, ~G, and ~k.)
    #
    # I've added pkcs7/x-pkcs7 to this, since it functions (for S/MIME)
    # analogously to PGP signature attachments. S/MIME isn't supported
    # in a stock NeoMutt build, but we can still treat it specially here.
    #
    attachments  +A */.*
    attachments  -A text/vcard text/x-vcard
    attachments  -A application/pgp.*
    attachments  -A application/pkcs7-.* application/x-pkcs7-.*
    # Discount all MIME parts with an "inline" disposition, unless they're
    # text/plain. (Why inline a text/plain part unless it's external to the
    # message flow?)
    attachments  +I text/plain
    # These two lines make NeoMutt qualify MIME containers. (So, for example,
    # a message/rfc822 forward will count as an attachment.) The first
    # line is unnecessary if you already have "attach-allow */.*", of
    # course. These are off by default! The MIME elements contained
    # within a message/* or multipart/* are still examined, even if the
    # containers themselves don't qualify.
    # Recursion into multipart/alternatives containers is controlled by the
    # $count_alternatives setting.

    #attachments  +A message/.* multipart/.*
    #attachments  +I message/.* multipart/.*
    ## You probably don't really care to know about deleted attachments.
    attachments  -A message/external-body
    attachments  -I message/external-body

Entering the command “attachments ?” as a command will list your current settings in neomuttrc format, so that it can be pasted elsewhere.

Entering the command “unattachments *” as a command will Clear all attachment settings.

## 9. MIME Lookup

Usage:

`mime_lookup` `mime-type` [ `/mime-subtype` ] [ `mime-type` [ `/mime-subtype` ] ...]
`unmime_lookup` { * | [ `mime-type` [ `/mime-subtype` ] ...]}

NeoMutt's mime_lookup list specifies a list of MIME types that should not be treated according to their mailcap entry. This option is designed to deal with binary types such as `application/octet-stream`. When an attachment's MIME type is listed in mime_lookup, then the extension of the filename will be compared to the list of extensions in the `mime.types` file. The MIME type associated with this extension will then be used to process the attachment according to the rules in the mailcap file and according to any other configuration options (such as auto_view) specified. Common usage would be:

    mime_lookup application/octet-stream application/X-Lotus-Manuscript

In addition, the `unmime_lookup` command may be used to disable this feature for any particular MIME type if it had been set, for example, in a global `.neomuttrc`.

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