Chapter 4. Advanced Usage
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## Chapter 4. Advanced Usage

## 1. Regular Expressions

All string patterns in Mutt including those in more complex patterns must be specified using regular expressions (regexp) in the ``POSIX extended'' syntax (which is more or less the syntax used by egrep and GNU awk). For your convenience, we have included below a brief description of this syntax.

The search is case sensitive if the pattern contains at least one upper case letter, and case insensitive otherwise. Note that ``\'' must be quoted if used for a regular expression in an initialization command: ``\\''.

A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions.

Note that the regular expression can be enclosed/delimited by either " or ' which is useful if the regular expression includes a white-space character. See Syntax of Initialization Files for more information on " and ' delimiter processing. To match a literal " or ' you must preface it with \ (backslash).

The fundamental building blocks are the regular expressions that match a single character. Most characters, including all letters and digits, are regular expressions that match themselves. Any metacharacter with special meaning may be quoted by preceding it with a backslash.

The period ``.'' matches any single character. The caret ``^'' and the dollar sign ``$'' are metacharacters that respectively match the empty string at the beginning and end of a line.

A list of characters enclosed by ``['' and ``]'' matches any single character in that list; if the first character of the list is a caret ``^'' then it matches any character not in the list. For example, the regular expression [0123456789] matches any single digit. A range of ASCII characters may be specified by giving the first and last characters, separated by a hyphen ``-''. Most metacharacters lose their special meaning inside lists. To include a literal ``]'' place it first in the list. Similarly, to include a literal ``^'' place it anywhere but first. Finally, to include a literal hyphen ``-'' place it last.

Certain named classes of characters are predefined. Character classes consist of ``[:'', a keyword denoting the class, and ``:]''. The following classes are defined by the POSIX standard:

[:alnum:]

  Alphanumeric characters.

[:alpha:]

  Alphabetic characters.

[:blank:]

  Space or tab characters.

[:cntrl:]

  Control characters.

[:digit:]

  Numeric characters.

[:graph:]

  Characters that are both printable and visible. (A space is printable, but not visible, while an ``a'' is both.)

[:lower:]

  Lower-case alphabetic characters.

[:print:]

  Printable characters (characters that are not control characters.)

[:punct:]

  Punctuation characters (characters that are not letter, digits, control characters, or space characters).

[:space:]

  Space characters (such as space, tab and formfeed, to name a few).

[:upper:]

  Upper-case alphabetic characters.

[:xdigit:]

  Characters that are hexadecimal digits.

A character class is only valid in a regular expression inside the brackets of a character list. Note that the brackets in these class names are part of the symbolic names, and must be included in addition to the brackets delimiting the bracket list. For example, [[:digit:]] is equivalent to [0-9].

Two additional special sequences can appear in character lists. These apply to non-ASCII character sets, which can have single symbols (called collating elements) that are represented with more than one character, as well as several characters that are equivalent for collating or sorting purposes:

Collating Symbols

  A collating symbol is a multi-character collating element enclosed in ``[.'' and ``.]''. For example, if ``ch'' is a collating element, then [[.ch.]] is a regexp that matches this collating element, while [ch] is a regexp that matches either ``c'' or ``h''.

Equivalence Classes

  An equivalence class is a locale-specific name for a list of characters that are equivalent. The name is enclosed in ``[='' and ``=]''. For example, the name ``e'' might be used to represent all of ``è'' ``é'' and ``e''. In this case, [[=e=]] is a regexp that matches any of ``è'', ``é'' and ``e''.

A regular expression matching a single character may be followed by one of several repetition operators:

?

  The preceding item is optional and matched at most once.

*

  The preceding item will be matched zero or more times.

+

  The preceding item will be matched one or more times.

{n}

  The preceding item is matched exactly n times.

{n,}

  The preceding item is matched n or more times.

{,m}

  The preceding item is matched at most m times.

{n,m}

  The preceding item is matched at least n times, but no more than m times.

Two regular expressions may be concatenated; the resulting regular expression matches any string formed by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator ``|''; the resulting regular expression matches any string matching either subexpression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation. A whole subexpression may be enclosed in parentheses to override these precedence rules.

Note: If you compile Mutt with the GNU rx package, the following operators may also be used in regular expressions:

\\y

  Matches the empty string at either the beginning or the end of a word.

\\B

  Matches the empty string within a word.

\\<

  Matches the empty string at the beginning of a word.

\\>

  Matches the empty string at the end of a word.

\\w

  Matches any word-constituent character (letter, digit, or underscore).

\\W

  Matches any character that is not word-constituent.

\\`

  Matches the empty string at the beginning of a buffer (string).

\\'

  Matches the empty string at the end of a buffer.

Please note however that these operators are not defined by POSIX, so they may or may not be available in stock libraries on various systems.

## 2. Patterns

Many of Mutt's commands allow you to specify a pattern to match (limit, tag-pattern, delete-pattern, etc.). There are several ways to select messages:

Table 4.1. Pattern modifiers

Pattern modifier | Description
--- | ---
~A | all messages
~b EXPR | messages which contain EXPR in the message body
~B EXPR | messages which contain EXPR in the whole message
~c EXPR | messages carbon-copied to EXPR
~C EXPR | message is either to: or cc: EXPR
~d [MIN]-[MAX] | messages with ``date-sent'' in a Date range
~D | deleted messages
~e EXPR | message which contains EXPR in the ``Sender'' field
~E | expired messages
~F | flagged messages
~f EXPR | messages originating from EXPR
~g | cryptographically signed messages
~G | cryptographically encrypted messages
~h EXPR | messages which contain EXPR in the message header
~H EXPR | messages with a spam attribute matching EXPR
~i EXPR | message which match EXPR in the ``Message-ID'' field
~k | message contains PGP key material
~L EXPR | message is either originated or received by EXPR
~l | message is addressed to a known mailing list
~m [MIN]-[MAX] | message in the range MIN to MAX *)
~n [MIN]-[MAX] | messages with a score in the range MIN to MAX *)
~N | new messages
~O | old messages
~p | message is addressed to you (consults alternates)
~P | message is from you (consults alternates)
~Q | messages which have been replied to
~r [MIN]-[MAX] | messages with ``date-received'' in a Date range
~R | read messages
~s EXPR | messages having EXPR in the ``Subject'' field.
~S | superseded messages
~t EXPR | messages addressed to EXPR
~T | tagged messages
~u | message is addressed to a subscribed mailing list
~U | unread messages
~v | message is part of a collapsed thread.
~V | cryptographically verified messages
~x EXPR | messages which contain EXPR in the `References' field
~X [MIN]-[MAX] | messages with MIN to MAX attachments *)
~y EXPR | messages which contain EXPR in the `X-Label' field
~z [MIN]-[MAX] | messages with a size in the range MIN to MAX *)
~= | duplicated messages (see $duplicate_threads)
~$ | unreferenced messages (requires threaded view)

Where EXPR is a regular expression. Special attention has to be made when using regular expressions inside of patterns. Specifically, Mutt's parser for these patterns will strip one level of backslash (\), which is normally used for quoting. If it is your intention to use a backslash in the regular expression, you will need to use two backslashes instead (\\). You can force mutt to treat EXPR as a simple string instead of a regular expression by using = instead of ˜ in the pattern name. For example, =b *.* will find all messages that contain the literal string '*.*'. Simple string matches are less powerful than regular expressions but can be considerably faster. This is especially true for IMAP folders, because string matches can be performed on the server instead of by fetching every message. IMAP treats =h specially: it must be of the form "header: substring" and will not partially match header names. The substring part may be omitted if you simply wish to find messages containing a particular header without regard to its value.

*) The forms `<[MAX]`, `>[MIN]`, `[MIN]-` and `-[MAX]` are allowed, too.

### 2.1. Pattern Modifier

Note that patterns matching 'lists' of addresses (notably c,C,p,P and t) match if there is at least one match in the whole list. If you want to make sure that all elements of that list match, you need to prefix your pattern with ^. This example matches all mails which only has recipients from Germany.

    ^~C \.de$

### 2.2. Complex Patterns

Logical AND is performed by specifying more than one criterion. For example:

    ~t mutt ~f elkins

would select messages which contain the word ``mutt'' in the list of recipients and that have the word ``elkins'' in the ``From'' header field.

Mutt also recognizes the following operators to create more complex search patterns:

- ! -- logical NOT operator

- | -- logical OR operator

- () -- logical grouping operator

Here is an example illustrating a complex search pattern. This pattern will select all messages which do not contain ``mutt'' in the ``To'' or ``Cc'' field and which are from ``elkins''.

    !(~t mutt|~c mutt) ~f elkins

Here is an example using white space in the regular expression (note the ' and " delimiters). For this to match, the mail's subject must match the ``^Junk +From +Me$'' and it must be from either ``Jim +Somebody'' or ``Ed +SomeoneElse'':

     '~s "^Junk +From +Me$" ~f ("Jim +Somebody"|"Ed +SomeoneElse")'

Note that if a regular expression contains parenthesis, or a vertical bar ("|"), you must enclose the expression in double or single quotes since those characters are also used to separate different parts of Mutt's pattern language. For example,

    ~f "me@(mutt\.org|cs\.hmc\.edu)"

Without the quotes, the parenthesis wouldn't end. This would be seperated to two OR'd patterns: ˜f me@(mutt\.org and cs\.hmc\.edu). They are never what you want.

### 2.3. Searching by Date

Mutt supports two types of dates, absolute and relative.

Absolute. Dates must be in DD/MM/YY format (month and year are optional, defaulting to the current month and year). An example of a valid range of dates is:

    Limit to messages matching: ~d 20/1/95-31/10

If you omit the minimum (first) date, and just specify ``-DD/MM/YY'', all messages before the given date will be selected. If you omit the maximum (second) date, and specify ``DD/MM/YY-'', all messages after the given date will be selected. If you specify a single date with no dash (``-''), only messages sent on the given date will be selected.

Error Margins. You can add error margins to absolute dates. An error margin is a sign (+ or -), followed by a digit, followed by one of the following units:

    y        years
    m        months
    w        weeks
    d        days

As a special case, you can replace the sign by a ``*'' character, which is equivalent to giving identical plus and minus error margins.

Example: To select any messages two weeks around January 15, 2001, you'd use the following pattern:

    Limit to messages matching: ~d 15/1/2001*2w

Relative. This type of date is relative to the current date, and may be specified as:

- >offset (messages older than offset units)

- <offset (messages newer than offset units)

- =offset (messages exactly offset units old)

offset is specified as a positive number with one of the following units:

    y       years
    m       months
    w       weeks
    d       days

Example: to select messages less than 1 month old, you would use

    Limit to messages matching: ~d <1m

Note: all dates used when searching are relative to the local time zone, so unless you change the setting of your $index_format to include a `%[...]` format, these are not the dates shown in the main index.

## 3. Using Tags

Sometimes it is desirable to perform an operation on a group of messages all at once rather than one at a time. An example might be to save messages to a mailing list to a separate folder, or to delete all messages with a given subject. To tag all messages matching a pattern, use the tag-pattern function, which is bound to ``shift-T'' by default. Or you can select individual messages by hand using the ``tag-message'' function, which is bound to ``t'' by default. See patterns for Mutt's pattern matching syntax.

Once you have tagged the desired messages, you can use the ``tag-prefix'' operator, which is the ``;'' (semicolon) key by default. When the ``tag-prefix'' operator is used, the next operation will be applied to all tagged messages if that operation can be used in that manner. If the $auto_tag variable is set, the next operation applies to the tagged messages automatically, without requiring the ``tag-prefix''.

In macros or push commands, you can use the ``tag-prefix-cond'' operator. If there are no tagged messages, mutt will "eat" the rest of the macro to abort it's execution. Mutt will stop "eating" the macro when it encounters the ``end-cond'' operator; after this operator the rest of the macro will be executed as normal.

## 4. Using Hooks

A hook is a concept borrowed from the EMACS editor which allows you to execute arbitrary commands before performing some operation. For example, you may wish to tailor your configuration based upon which mailbox you are reading, or to whom you are sending mail. In the Mutt world, a hook consists of a regular expression or pattern along with a configuration option/command. See

- folder-hook

- send-hook

- message-hook

- save-hook

- mbox-hook

- fcc-hook

- fcc-save-hook

for specific details on each type of hook available.

Note: if a hook changes configuration settings, these changes remain effective until the end of the current mutt session. As this is generally not desired, a default hook needs to be added before all other hooks to restore configuration defaults. Here is an example with send-hook and the my_hdr directive:

    send-hook . 'unmy_hdr From:'
    send-hook ~C'^b@b\.b$' my_hdr from: c@c.c

### 4.1. Message Matching in Hooks

Hooks that act upon messages (`send-hook, save-hook, fcc-hook, message-hook`) are evaluated in a slightly different manner. For the other types of hooks, a regular expression is sufficient. But in dealing with messages a finer grain of control is needed for matching since for different purposes you want to match different criteria.

Mutt allows the use of the search pattern language for matching messages in hook commands. This works in exactly the same way as it would when limiting or searching the mailbox, except that you are restricted to those operators which match information mutt extracts from the header of the message (i.e. from, to, cc, date, subject, etc.).

For example, if you wanted to set your return address based upon sending mail to a specific address, you could do something like:

    send-hook '~t ^me@cs\.hmc\.edu$' 'my_hdr From: Mutt User <user@host>'

which would execute the given command when sending mail to me@cs.hmc.edu.

However, it is not required that you write the pattern to match using the full searching language. You can still specify a simple regular expression like the other hooks, in which case Mutt will translate your pattern into the full language, using the translation specified by the $default_hook variable. The pattern is translated at the time the hook is declared, so the value of $default_hook that is in effect at that time will be used.

## 5. External Address Queries

Mutt supports connecting to external directory databases such as LDAP, ph/qi, bbdb, or NIS through a wrapper script which connects to mutt using a simple interface. Using the $query_command variable, you specify the wrapper command to use. For example:

    set query_command = "mutt_ldap_query.pl '%s'"

The wrapper script should accept the query on the command-line. It should return a one line message, then each matching response on a single line, each line containing a tab separated address then name then some other optional information. On error, or if there are no matching addresses, return a non-zero exit code and a one line error message.

An example multiple response output:

    Searching database ... 20 entries ... 3 matching:
    me@cs.hmc.edu           Michael Elkins  mutt dude
    blong@fiction.net       Brandon Long    mutt and more
    roessler@guug.de        Thomas Roessler mutt pgp

There are two mechanisms for accessing the query function of mutt. One is to do a query from the index menu using the query function (default: Q). This will prompt for a query, then bring up the query menu which will list the matching responses. From the query menu, you can select addresses to create aliases, or to mail. You can tag multiple addresses to mail, start a new query, or have a new query appended to the current responses.

The other mechanism for accessing the query function is for address completion, similar to the alias completion. In any prompt for address entry, you can use the complete-query function (default: ^T) to run a query based on the current address you have typed. Like aliases, mutt will look for what you have typed back to the last space or comma. If there is a single response for that query, mutt will expand the address in place. If there are multiple responses, mutt will activate the query menu. At the query menu, you can select one or more addresses to be added to the prompt.

## 6. Mailbox Formats

Mutt supports reading and writing of four different mailbox formats: mbox, MMDF, MH and Maildir. The mailbox type is autodetected, so there is no need to use a flag for different mailbox types. When creating new mailboxes, Mutt uses the default specified with the $mbox_type variable.

mbox. This is the most widely used mailbox format for UNIX. All messages are stored in a single file. Each message has a line of the form:

    From me@cs.hmc.edu Fri, 11 Apr 1997 11:44:56 PST

to denote the start of a new message (this is often referred to as the ``From_'' line).

MMDF. This is a variant of the mbox format. Each message is surrounded by lines containing ``^A^A^A^A'' (four control-A's).

MH. A radical departure from mbox and MMDF, a mailbox consists of a directory and each message is stored in a separate file. The filename indicates the message number (however, this is may not correspond to the message number Mutt displays). Deleted messages are renamed with a comma (,) prepended to the filename. Note: Mutt detects this type of mailbox by looking for either `.mh_sequences` or `.xmhcache` (needed to distinguish normal directories from MH mailboxes).

Maildir. The newest of the mailbox formats, used by the Qmail MTA (a replacement for sendmail). Similar to MH, except that it adds three subdirectories of the mailbox: tmp, new and cur. Filenames for the messages are chosen in such a way they are unique, even when two programs are writing the mailbox over NFS, which means that no file locking is needed.

## 7. Mailbox Shortcuts

There are a number of built in shortcuts which refer to specific mailboxes. These shortcuts can be used anywhere you are prompted for a file or mailbox path.

- ! -- refers to your $spoolfile (incoming) mailbox

- > -- refers to your $mbox file

- < -- refers to your $record file

- ^ -- refers to the current mailbox

- - or !! -- refers to the file you've last visited

- ˜ -- refers to your home directory

- = or + -- refers to your $folder directory

- @alias -- refers to the default save folder as determined by the address of the alias

## 8. Handling Mailing Lists

Mutt has a few configuration options that make dealing with large amounts of mail easier. The first thing you must do is to let Mutt know what addresses you consider to be mailing lists (technically this does not have to be a mailing list, but that is what it is most often used for), and what lists you are subscribed to. This is accomplished through the use of the lists and subscribe commands in your muttrc.

Now that Mutt knows what your mailing lists are, it can do several things, the first of which is the ability to show the name of a list through which you received a message (i.e., of a subscribed list) in the index menu display. This is useful to distinguish between personal and list mail in the same mailbox. In the $index_format variable, the escape ``%L'' will return the string ``To <list>'' when ``list'' appears in the ``To'' field, and ``Cc <list>'' when it appears in the ``Cc'' field (otherwise it returns the name of the author).

Often times the ``To'' and ``Cc'' fields in mailing list messages tend to get quite large. Most people do not bother to remove the author of the message they are reply to from the list, resulting in two or more copies being sent to that person. The ``list-reply'' function, which by default is bound to ``L'' in the index menu and pager, helps reduce the clutter by only replying to the known mailing list addresses instead of all recipients (except as specified by `Mail-Followup-To`, see below).

Mutt also supports the `Mail-Followup-To` header. When you send a message to a list of recipients which includes one or several subscribed mailing lists, and if the $followup_to option is set, mutt will generate a Mail-Followup-To header which contains all the recipients to whom you send this message, but not your address. This indicates that group-replies or list-replies (also known as ``followups'') to this message should only be sent to the original recipients of the message, and not separately to you - you'll receive your copy through one of the mailing lists you are subscribed to.

Conversely, when group-replying or list-replying to a message which has a `Mail-Followup-To` header, mutt will respect this header if the $honor_followup_to configuration variable is set. Using list-reply will in this case also make sure that the reply goes to the mailing list, even if it's not specified in the list of recipients in the `Mail-Followup-To`.

Note that, when header editing is enabled, you can create a `Mail-Followup-To` header manually. Mutt will only auto-generate this header if it doesn't exist when you send the message.

The other method some mailing list admins use is to generate a ``Reply-To'' field which points back to the mailing list address rather than the author of the message. This can create problems when trying to reply directly to the author in private, since most mail clients will automatically reply to the address given in the ``Reply-To'' field. Mutt uses the $reply_to variable to help decide which address to use. If set to ask-yes or ask-no, you will be prompted as to whether or not you would like to use the address given in the ``Reply-To'' field, or reply directly to the address given in the ``From'' field. When set to yes, the ``Reply-To'' field will be used when present.

The ``X-Label:'' header field can be used to further identify mailing lists or list subject matter (or just to annotate messages individually). The $index_format variable's ``%y'' and ``%Y'' escapes can be used to expand ``X-Label:'' fields in the index, and Mutt's pattern-matcher can match regular expressions to ``X-Label:'' fields with the ``˜y'' selector. ``X-Label:'' is not a standard message header field, but it can easily be inserted by procmail and other mail filtering agents.

Lastly, Mutt has the ability to sort the mailbox into threads. A thread is a group of messages which all relate to the same subject. This is usually organized into a tree-like structure where a message and all of its replies are represented graphically. If you've ever used a threaded news client, this is the same concept. It makes dealing with large volume mailing lists easier because you can easily delete uninteresting threads and quickly find topics of value.

## 9. Editing threads

Mutt has the ability to dynamically restructure threads that are broken either by misconfigured software or bad behaviour from some correspondents. This allows to clean your mailboxes formats) from these annoyances which make it hard to follow a discussion.

### 9.1. Linking threads

Some mailers tend to "forget" to correctly set the "In-Reply-To:" and "References:" headers when replying to a message. This results in broken discussions because Mutt has not enough information to guess the correct threading. You can fix this by tagging the reply, then moving to the parent message and using the ``link-threads'' function (bound to & by default). The reply will then be connected to this "parent" message.

You can also connect multiple childs at once, tagging them and using the tag-prefix command (';') or the auto_tag option.

### 9.2. Breaking threads

On mailing lists, some people are in the bad habit of starting a new discussion by hitting "reply" to any message from the list and changing the subject to a totally unrelated one. You can fix such threads by using the ``break-thread'' function (bound by default to #), which will turn the subthread starting from the current message into a whole different thread.

## 10. Delivery Status Notification (DSN) Support

RFC1894 defines a set of MIME content types for relaying information about the status of electronic mail messages. These can be thought of as ``return receipts.'' Berkeley sendmail 8.8.x currently has some command line options in which the mail client can make requests as to what type of status messages should be returned.

To support this, there are two variables. $dsn_notify is used to request receipts for different results (such as failed message, message delivered, etc.). $dsn_return requests how much of your message should be returned with the receipt (headers or full message). Refer to the man page on sendmail for more details on DSN.

## 11. POP3 Support (OPTIONAL)

If Mutt was compiled with POP3 support (by running the configure script with the --enable-pop flag), it has the ability to work with mailboxes located on a remote POP3 server and fetch mail for local browsing.

You can access the remote POP3 mailbox by selecting the folder `pop://popserver/`.

You can select an alternative port by specifying it with the server, ie: `pop://popserver:port/`.

You can also specify different username for each folder, ie: `pop://username@popserver[:port]/`.

Polling for new mail is more expensive over POP3 than locally. For this reason the frequency at which Mutt will check for mail remotely can be controlled by the $pop_checkinterval variable, which defaults to every 60 seconds.

If Mutt was compiled with SSL support (by running the configure script with the --with-ssl flag), connections to POP3 servers can be encrypted. This naturally requires that the server supports SSL encrypted connections. To access a folder with POP3/SSL, you should use pops: prefix, ie: `pops://[username@]popserver[:port]/`.

Another way to access your POP3 mail is the fetch-mail function (default: G). It allows to connect to $pop_host, fetch all your new mail and place it in the local $spoolfile. After this point, Mutt runs exactly as if the mail had always been local.

Note: If you only need to fetch all messages to local mailbox you should consider using a specialized program, such as fetchmail

## 12. IMAP Support (OPTIONAL)

If Mutt was compiled with IMAP support (by running the configure script with the --enable-imap flag), it has the ability to work with folders located on a remote IMAP server.

You can access the remote inbox by selecting the folder `imap://imapserver/INBOX`, where `imapserver` is the name of the IMAP server and `INBOX` is the special name for your spool mailbox on the IMAP server. If you want to access another mail folder at the IMAP server, you should use `imap://imapserver/path/to/folder` where `path/to/folder` is the path of the folder you want to access.

You can select an alternative port by specifying it with the server, ie: `imap://imapserver:port/INBOX`.

You can also specify different username for each folder, ie: `imap://username@imapserver[:port]/INBOX`.

If Mutt was compiled with SSL support (by running the configure script with the --with-ssl flag), connections to IMAP servers can be encrypted. This naturally requires that the server supports SSL encrypted connections. To access a folder with IMAP/SSL, you should use `imaps://[username@]imapserver[:port]/path/to/folder` as your folder path.

Pine-compatible notation is also supported, ie `{[username@]imapserver[:port][/ssl]}path/to/folder`

Note that not all servers use / as the hierarchy separator. Mutt should correctly notice which separator is being used by the server and convert paths accordingly.

When browsing folders on an IMAP server, you can toggle whether to look at only the folders you are subscribed to, or all folders with the toggle-subscribed command. See also the $imap_list_subscribed variable.

Polling for new mail on an IMAP server can cause noticeable delays. So, you'll want to carefully tune the $mail_check and $timeout variables. Personally I use

    set mail_check=90
    set timeout=15

with relatively good results over my slow modem line.

Note that if you are using mbox as the mail store on UW servers prior to v12.250, the server has been reported to disconnect a client if another client selects the same folder.

### 12.1. The Folder Browser

As of version 1.2, mutt supports browsing mailboxes on an IMAP server. This is mostly the same as the local file browser, with the following differences:

- In lieu of file permissions, mutt displays the string "IMAP", possibly followed by the symbol "+", indicating that the entry contains both messages and subfolders. On Cyrus-like servers folders will often contain both messages and subfolders.

- For the case where an entry can contain both messages and subfolders, the selection key (bound to `enter` by default) will choose to descend into the subfolder view. If you wish to view the messages in that folder, you must use `view-file` instead (bound to `space` by default).

- You can create, delete and rename mailboxes with the `create-mailbox`, `delete-mailbox`, and `rename-mailbox` commands (default bindings: `C`, `d` and `r`, respectively). You may also `subscribe` and `unsubscribe` to mailboxes (normally these are bound to `s` and `u`, respectively).

### 12.2. Authentication

Mutt supports four authentication methods with IMAP servers: SASL, GSSAPI, CRAM-MD5, and LOGIN (there is a patch by Grant Edwards to add NTLM authentication for you poor exchange users out there, but it has yet to be integrated into the main tree). There is also support for the pseudo-protocol ANONYMOUS, which allows you to log in to a public IMAP server without having an account. To use ANONYMOUS, simply make your username blank or "anonymous".

SASL is a special super-authenticator, which selects among several protocols (including GSSAPI, CRAM-MD5, ANONYMOUS, and DIGEST-MD5) the most secure method available on your host and the server. Using some of these methods (including DIGEST-MD5 and possibly GSSAPI), your entire session will be encrypted and invisible to those teeming network snoops. It is the best option if you have it. To use it, you must have the Cyrus SASL library installed on your system and compile mutt with the --with-sasl flag.

Mutt will try whichever methods are compiled in and available on the server, in the following order: SASL, ANONYMOUS, GSSAPI, CRAM-MD5, LOGIN.

There are a few variables which control authentication:

- $imap_user - controls the username under which you request authentication on the IMAP server, for all authenticators. This is overridden by an explicit username in the mailbox path (ie by using a mailbox name of the form `{user@host}`).

- $imap_pass - a password which you may preset, used by all authentication methods where a password is needed.

- $imap_authenticators - a colon-delimited list of IMAP authentication methods to try, in the order you wish to try them. If specified, this overrides mutt's default (attempt everything, in the order listed above).

## 13. Managing multiple IMAP/POP accounts (OPTIONAL)

If you happen to have accounts on multiple IMAP and/or POP servers, you may find managing all the authentication settings inconvenient and error-prone. The account-hook command may help. This hook works like folder-hook but is invoked whenever you access a remote mailbox (including inside the folder browser), not just when you open the mailbox.

Some examples:

    account-hook . 'unset imap_user; unset imap_pass; unset tunnel'
    account-hook imap://host1/ 'set imap_user=me1 imap_pass=foo'
    account-hook imap://host2/ 'set tunnel="ssh host2 /usr/libexec/imapd"'

## 14. Start a WWW Browser on URLs (EXTERNAL)

If a message contains URLs (unified resource locator = address in the WWW space like http://www.mutt.org/), it is efficient to get a menu with all the URLs and start a WWW browser on one of them. This functionality is provided by the external urlview program which can be retrieved at ftp://ftp.mutt.org/mutt/contrib/ and the configuration commands:

    macro index \cb |urlview\n
    macro pager \cb |urlview\n

## 15. Local caching (OPTIONAL)

Mutt contains two types of local caching: (1) the so-called ``header caching'' and (2) the so-called ``body caching'' which are both described in this section.

These are optional which means they're not enabled by default. Details on how to enable either of these techniques are given in the following subsections.

### 15.1. Header caching

Mutt provides optional support for caching message headers for the following types of folders: IMAP, POP, Maildir and MH. Header caching greatly improves speed because for remote folders, headers usually only need to be downloaded once. For Maildir and MH, reading the headers from a single file is much faster than looking at possibly thousands of single files (since Maildir and MH use one file per message.)

Header caching can be enabled via the configure script and the --enable--hcache option. It's not turned on by default because external database libraries are required: one of qdbm, gdbm or bdb must be present.

If enabled, $header_cache can be used to either point to a file or a directory. If set to point to a file, one database file for all folders will be used (which may result in lower performance), but one file per folder if it points to a directory.

For the one-file-per-folder case, database files will be named by MD5 sums. They may be safely removed if a system is short on space. You can compute the name of the header cache file for a particular folder through a command like the following:

    $ printf '%s' '/path/to/folder' | md5sum
    $ printf '%s' 'imaps://user@host/path/to/folder' | md5sum
    $ printf '%s' 'pops://user@host' | md5sum

The `md5sum` command may also be named `md5`, depending on your operating system.

### 15.2. Body caching

In addition to caching message headers only, mutt can also cache whole message bodies. This results in faster display of messages for POP and IMAP folders because messages usually have to be downloaded only once.

If the configure script is called with --enable-pop and/or --enable-imap, body caching will be built in as it does not require additional software packages such as database libraries.

For configuration, the variable $message_cachedir must point to a directory. There, mutt will create a hierarchy of subdirectories named like: `proto:user@hostname` where `proto` is either ``pop'' or ``imap.'' Within there for each folder, mutt stores messages in single files (just like Maildir) so that with manual symlink creation these cache directories can be examined with mutt as read-only Maildir folders.

All files can be removed as needed if the consumed disk space becomes an issue as mutt will silently fetch missing items again.

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