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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 6. Optional features</title><meta name="generator" content="DocBook XSL Stylesheets V1.72.0" /><link rel="start" href="index.html" title="The Mutt E-Mail Client" /><link rel="up" href="index.html" title="The Mutt E-Mail Client" /><link rel="prev" href="mimesupport.html" title="Chapter 5. Mutt's MIME Support" /><link rel="next" href="tuning.html" title="Chapter 7. Performance tuning" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 6. Optional features</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="mimesupport.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="tuning.html">Next</a></td></tr></table><hr /></div><div class="chapter" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title"><a id="optionalfeatures"></a>Chapter 6. Optional features</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="optionalfeatures.html#id2564897">1. General notes</a></span></dt><dd><dl><dt><span class="sect2"><a href="optionalfeatures.html#id2564903">1.1. Enabling/disabling features</a></span></dt><dt><span class="sect2"><a href="optionalfeatures.html#url-syntax">1.2. URL syntax</a></span></dt></dl></dd><dt><span class="sect1"><a href="optionalfeatures.html#ssl">2. SSL/TLS Support</a></span></dt><dt><span class="sect1"><a href="optionalfeatures.html#pop">3. POP3 Support</a></span></dt><dt><span class="sect1"><a href="optionalfeatures.html#imap">4. IMAP Support</a></span></dt><dd><dl><dt><span class="sect2"><a href="optionalfeatures.html#id2565327">4.1. The Folder Browser</a></span></dt><dt><span class="sect2"><a href="optionalfeatures.html#id2565449">4.2. Authentication</a></span></dt></dl></dd><dt><span class="sect1"><a href="optionalfeatures.html#smtp">5. SMTP Support</a></span></dt><dt><span class="sect1"><a href="optionalfeatures.html#account-hook">6. Managing multiple accounts</a></span></dt><dt><span class="sect1"><a href="optionalfeatures.html#caching">7. Local caching</a></span></dt><dd><dl><dt><span class="sect2"><a href="optionalfeatures.html#header-caching">7.1. Header caching</a></span></dt><dt><span class="sect2"><a href="optionalfeatures.html#body-caching">7.2. Body caching</a></span></dt></dl></dd></dl></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2564897"></a>1. General notes</h2></div></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2564903"></a>1.1. Enabling/disabling features</h3></div></div></div><p>
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Mutt supports several of optional features which can be enabled or
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disabled at compile-time by giving the <span class="emphasis"><em>configure</em></span> script
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certain arguments. These are listed in the ``Optional features'' section of
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the <span class="emphasis"><em>configure --help</em></span> output.
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Which features are enabled or disabled can later be determined from the
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output of <code class="literal">mutt -v</code>. If a compile option starts with
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``+'' it is enabled and disabled if prefixed with ``-''. For example, if
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mutt was compiled using GnuTLS for encrypted communication instead of
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OpenSSL, <code class="literal">mutt -v</code> would contain:
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</p><pre class="screen">
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-USE_SSL_OPENSSL +USE_SSL_GNUTLS</pre></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="url-syntax"></a>1.2. URL syntax</h3></div></div></div><p>
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Mutt optionally supports the IMAP, POP3 and SMTP protocols which require
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to access servers using URLs. The canonical syntax for specifying URLs
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in mutt is (an item enclosed in <code class="literal">[]</code> means it is optional and
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</p><pre class="screen">
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proto[s]://[username[:password]@]server[:port]/[path]
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<code class="literal">proto</code> is the communication protocol:
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<code class="literal">imap</code> for IMAP, <code class="literal">pop</code> for POP3 and
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<code class="literal">smtp</code> for SMTP. If ``s'' for ``secure communication''
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is appended, mutt will attempt to establish an encrypted communication
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using SSL or TLS. If no explicit port is given, mutt will use the
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system's default for the given protocol.
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Since all protocols by mutt support authentication, the username may be
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given directly in the URL instead of using the <code class="literal">pop_user</code> or
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<code class="literal">imap_user</code> variables. A password can be given, too but
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is not recommended if the URL is specified in a configuration file on
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The optional path is only relevant for IMAP.
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For IMAP for example, you can select an alternative port by specifying it with the
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server: <code class="literal">imap://imapserver:port/INBOX</code>. You can also specify different
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username for each folder: <code class="literal">imap://username@imapserver[:port]/INBOX</code>
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or <code class="literal">imap://username2@imapserver[:port]/path/to/folder</code>.
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Replacing <code class="literal">imap://</code> by <code class="literal">imaps://</code>
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would make mutt attempt to conect using SSL or TLS on a different port
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to encrypt the communication.
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</p></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="ssl"></a>2. SSL/TLS Support</h2></div></div></div><p>
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If mutt is compiled with IMAP, POP3 and/or SMTP support, it can also be
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compiled with support for SSL or TLS using either OpenSSL or GnuTLS (
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by running the <span class="emphasis"><em>configure</em></span> script with the
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<span class="emphasis"><em>--enable-ssl=...</em></span> option for OpenSSL or
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<span class="emphasis"><em>--enable-gnutls=...</em></span> for GnuTLS). Mutt can then
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attempt to encrypt communication with remote servers if these protocols
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are suffixed with ``s'' for ``secure communication''.
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</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="pop"></a>3. POP3 Support</h2></div></div></div><p>
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If Mutt was compiled with POP3 support (by running the <span class="emphasis"><em>configure</em></span>
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script with the <span class="emphasis"><em>--enable-pop</em></span> flag), it has the ability to work
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with mailboxes located on a remote POP3 server and fetch mail for local
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Remote POP3 servers can be accessed using URLs with the <code class="literal">pop</code> protocol
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for unencrypted and <code class="literal">pops</code> for encrypted
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communication, see <a href="optionalfeatures.html#url-syntax" title="1.2. URL syntax">Section 1.2, “URL syntax”</a> for details.
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Polling for new mail is more expensive over POP3 than locally. For this
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reason the frequency at which Mutt will check for mail remotely can be
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<a href="reference.html#pop-checkinterval" title="3.215. pop_checkinterval">$pop_checkinterval</a>
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variable, which defaults to every 60 seconds.
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Another way to access your POP3 mail is the <span class="emphasis"><em>fetch-mail</em></span> function
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(default: G). It allows to connect to <a href="reference.html#pop-host" title="3.217. pop_host">$pop_host</a>, fetch all your new mail and place it in the
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local <a href="reference.html#spoolfile" title="3.275. spoolfile">$spoolfile</a>. After this
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point, Mutt runs exactly as if the mail had always been local.
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<span class="bold"><strong>Note:</strong></span> If you only need to fetch all messages to a
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local mailbox you should consider using a specialized program, such as
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<code class="literal">fetchmail</code>, <code class="literal">getmail</code> or similar.
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</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="imap"></a>4. IMAP Support</h2></div></div></div><p>
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If Mutt was compiled with IMAP support (by running the <span class="emphasis"><em>configure</em></span>
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script with the <span class="emphasis"><em>--enable-imap</em></span> flag), it has the ability to work
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with folders located on a remote IMAP server.
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You can access the remote inbox by selecting the folder by its URL
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(see <a href="optionalfeatures.html#url-syntax" title="1.2. URL syntax">Section 1.2, “URL syntax”</a> for details) using the
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<code class="literal">imap</code> or <code class="literal">imaps</code> protocol.
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Alternatively, a pine-compatible notation is also supported, ie
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<code class="literal">{[username@]imapserver[:port][/ssl]}path/to/folder</code>
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Note that not all servers use ``/'' as the hierarchy separator. Mutt should
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correctly notice which separator is being used by the server and convert
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When browsing folders on an IMAP server, you can toggle whether to look
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at only the folders you are subscribed to, or all folders with the
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<span class="emphasis"><em>toggle-subscribed</em></span> command. See also the
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<a href="reference.html#imap-list-subscribed" title="3.89. imap_list_subscribed">$imap_list_subscribed</a> variable.
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Polling for new mail on an IMAP server can cause noticeable delays. So, you'll
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want to carefully tune the
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<a href="reference.html#mail-check" title="3.104. mail_check">$mail_check</a>
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<a href="reference.html#timeout" title="3.285. timeout">$timeout</a>
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variables. Personally I use
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</p><pre class="screen">
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with relatively good results over my slow modem line.
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Note that if you are using mbox as the mail store on UW servers prior to
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v12.250, the server has been reported to disconnect a client if another client
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selects the same folder.
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</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2565327"></a>4.1. The Folder Browser</h3></div></div></div><p>
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As of version 1.2, mutt supports browsing mailboxes on an IMAP
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server. This is mostly the same as the local file browser, with the
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following differences:
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</p><div class="itemizedlist"><ul type="disc"><li><p>
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In lieu of file permissions, mutt displays the string "IMAP",
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possibly followed by the symbol "+", indicating
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that the entry contains both messages and subfolders. On
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Cyrus-like servers folders will often contain both messages and
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For the case where an entry can contain both messages and
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subfolders, the selection key (bound to <code class="literal">enter</code> by default)
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will choose to descend into the subfolder view. If you wish to view
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the messages in that folder, you must use <code class="literal">view-file</code> instead
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(bound to <code class="literal">space</code> by default).
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You can create, delete and rename mailboxes with the
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<code class="literal">create-mailbox</code>, <code class="literal">delete-mailbox</code>, and
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<code class="literal">rename-mailbox</code> commands (default bindings: <code class="literal">C</code>,
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<code class="literal">d</code> and <code class="literal">r</code>, respectively). You may also
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<code class="literal">subscribe</code> and <code class="literal">unsubscribe</code> to mailboxes (normally
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these are bound to <code class="literal">s</code> and <code class="literal">u</code>, respectively).
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</p></li></ul></div><p>
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</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2565449"></a>4.2. Authentication</h3></div></div></div><p>
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Mutt supports four authentication methods with IMAP servers: SASL,
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GSSAPI, CRAM-MD5, and LOGIN (there is a patch by Grant Edwards to add
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NTLM authentication for you poor exchange users out there, but it has
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yet to be integrated into the main tree). There is also support for
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the pseudo-protocol ANONYMOUS, which allows you to log in to a public
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IMAP server without having an account. To use ANONYMOUS, simply make
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your username blank or "anonymous".
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SASL is a special super-authenticator, which selects among several protocols
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(including GSSAPI, CRAM-MD5, ANONYMOUS, and DIGEST-MD5) the most secure
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method available on your host and the server. Using some of these methods
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(including DIGEST-MD5 and possibly GSSAPI), your entire session will be
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encrypted and invisible to those teeming network snoops. It is the best
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option if you have it. To use it, you must have the Cyrus SASL library
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installed on your system and compile mutt with the <span class="emphasis"><em>--with-sasl</em></span> flag.
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Mutt will try whichever methods are compiled in and available on the server,
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in the following order: SASL, ANONYMOUS, GSSAPI, CRAM-MD5, LOGIN.
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There are a few variables which control authentication:
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</p><div class="itemizedlist"><ul type="disc"><li><p>
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<a href="reference.html#imap-user" title="3.95. imap_user">$imap_user</a> - controls
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the username under which you request authentication on the IMAP server,
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for all authenticators. This is overridden by an explicit username in
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the mailbox path (ie by using a mailbox name of the form
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<code class="literal">{user@host}</code>).
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<a href="reference.html#imap-pass" title="3.91. imap_pass">$imap_pass</a> - a
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password which you may preset, used by all authentication methods where
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a password is needed.
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<a href="reference.html#imap-authenticators" title="3.83. imap_authenticators">$imap_authenticators</a> - a colon-delimited list of IMAP
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authentication methods to try, in the order you wish to try them. If
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specified, this overrides mutt's default (attempt everything, in the order
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</p></li></ul></div><p>
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</p></div></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="smtp"></a>5. SMTP Support</h2></div></div></div><p>
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Besides supporting traditional mail delivery through a
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sendmail-compatible program, mutt supports delivery through SMTP if it
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was configured and built with <code class="literal">--enable-smtp</code>.
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If the configuration variable
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<a href="reference.html#smtp-url" title="3.268. smtp_url">$smtp_url</a> is set, mutt
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will contact the given SMTP server to deliver messages; if it is unset,
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mutt will use the program specified by <a href="reference.html#sendmail" title="3.256. sendmail">$sendmail</a>.
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For details on the URL syntax, please see <a href="optionalfeatures.html#url-syntax" title="1.2. URL syntax">Section 1.2, “URL syntax”</a>.
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The built-in SMTP support supports encryption (the <code class="literal">smtps</code> protocol
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using SSL or TLS) as well as SMTP authentication using SASL. The authentication mechanisms
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for SASL are specified in <a href="reference.html#smtp-authenticators" title="3.266. smtp_authenticators">$smtp_authenticators</a>
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defaulting to an empty list which makes mutt try all available methods
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from most-secure to least-secure.
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</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="account-hook"></a>6. Managing multiple accounts</h2></div></div></div><p>
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If you happen to have accounts on multiple IMAP, POP and/or SMTP servers,
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you may find managing all the authentication settings inconvenient and
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error-prone. The account-hook command may help. This hook works like
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folder-hook but is invoked whenever you access a remote mailbox
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(including inside the folder browser), not just when you open the
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</p><pre class="screen">
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account-hook . 'unset imap_user; unset imap_pass; unset tunnel'
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account-hook imap://host1/ 'set imap_user=me1 imap_pass=foo'
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account-hook imap://host2/ 'set tunnel="ssh host2 /usr/libexec/imapd"'
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account-hook smtp://user@host3/ 'set tunnel="ssh host3 /usr/libexec/smtpd"'
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</p></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="caching"></a>7. Local caching</h2></div></div></div><p>
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Mutt contains two types of local caching: <span class="emphasis"><em>(1)</em></span>
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the so-called ``header caching'' and <span class="emphasis"><em>(2)</em></span> the
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so-called ``body caching'' which are both described in this section.
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These are optional which means they're not enabled by default.
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Details on how to enable either of these techniques are given in the
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following subsections.
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</p><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="header-caching"></a>7.1. Header caching</h3></div></div></div><p>
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Mutt provides optional support for caching message headers for the
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following types of folders: IMAP, POP, Maildir and MH. Header caching
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greatly improves speed because for remote folders, headers
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usually only need to be downloaded once. For Maildir and MH, reading the
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headers from a single file is much faster than looking at possibly
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thousands of single files (since Maildir and MH use one file per message.)
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Header caching can be enabled via the configure script and the
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<span class="emphasis"><em>--enable-hcache</em></span> option. It's not turned on
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by default because external database libraries are required: one
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of qdbm, gdbm or bdb must be present.
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If enabled, <a href="reference.html#header-cache" title="3.107. header_cache">$header_cache</a> can be
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used to either point to a file or a directory. If set to point to
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a file, one database file for all folders will be used (which may
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result in lower performance), but one file per folder if it points
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For the one-file-per-folder case, database files will be named by MD5
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sums. They may be safely removed if a system is short on space. You
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can compute the name of the header cache file for a particular folder
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through a command like the following:
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</p><pre class="screen">
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$ printf '%s' '/path/to/folder' | md5sum
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$ printf '%s' 'imaps://user@host/path/to/folder' | md5sum
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$ printf '%s' 'pops://user@host' | md5sum
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The <code class="literal">md5sum</code> command may also be
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named <code class="literal">md5</code>, depending on your operating system.
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</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="body-caching"></a>7.2. Body caching</h3></div></div></div><p>
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In addition to caching message headers only, mutt can also cache
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whole message bodies. This results in faster display of messages
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for POP and IMAP folders because messages usually have to be
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downloaded only once.
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If the configure script is called with <span class="emphasis"><em>--enable-pop</em></span>
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and/or <span class="emphasis"><em>--enable-imap</em></span>, body caching will be
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built in as it does not require additional software packages such
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as database libraries.
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For configuration, the variable <a href="reference.html#message-cachedir" title="3.132. message_cachedir">$message_cachedir</a> must point to a
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directory. There, mutt will create a hierarchy of subdirectories
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named like: <code class="literal">proto:user@hostname</code> where
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<code class="literal">proto</code> is either ``pop'' or ``imap.'' Within
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there for each folder, mutt stores messages in single files (just
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like Maildir) so that with manual symlink creation these cache
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directories can be examined with mutt as read-only Maildir folders.
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All files can be removed as needed if the consumed disk space
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becomes an issue as mutt will silently fetch missing items again.
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</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="mimesupport.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="tuning.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 5. Mutt's MIME Support </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 7. Performance tuning</td></tr></table></div></body></html>
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