EVOLUTION-MANAGER
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<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><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 V1.78.1" /><link rel="home" 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="security.html" title="Chapter 7. Security Considerations" /><style xmlns="" type="text/css"> body { margin-left:2%; margin-right:2%; font-family:serif; } .toc, .list-of-tables, .list-of-examples { font-family:sans-serif; } h1, h2, h3, h4, h5, h6 { font-family:sans-serif; } p { text-align:justify; } div.table p.title, div.example p.title { font-size:smaller; font-family:sans-serif; } .email, .email a { font-family:monospace; } div.table-contents table, div.informaltable table { border-collapse:collapse; border:1px solid #c0c0c0; } div.table-contents table td, div.informaltable td, div.table-contents table th, div.informaltable table th { padding:5px; text-align:left; } div.table-contents table th, div.informaltable table th { font-family:sans-serif; background:#d0d0d0; font-weight:normal; vertical-align:top; } div.cmdsynopsis { border-left:1px solid #707070; padding-left:5px; } li div.cmdsynopsis { border-left:none; padding-left:0px; } pre.screen, div.note { background:#f0f0f0; border:1px solid #c0c0c0; padding:5px; margin-left:2%; margin-right:2%; } div.example p.title { margin-left:2%; } div.note h3 { font-size:small; font-style:italic; font-variant: small-caps; } div.note h3:after { content: ":" } div.note { margin-bottom: 5px; } .command { font-family: monospace; font-weight: normal; } .command strong { font-weight: normal; } tr { vertical-align: top; } .comment { color:#707070; } </style></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="security.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a id="optionalfeatures"></a>Chapter 6. Optional Features</h1></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="optionalfeatures.html#optionalfeatures-notes">1. General Notes</a></span></dt><dd><dl><dt><span class="sect2"><a href="optionalfeatures.html#compile-time-features">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#imap-browser">4.1. The IMAP Folder Browser</a></span></dt><dt><span class="sect2"><a href="optionalfeatures.html#imap-authentication">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><dt><span class="sect2"><a href="optionalfeatures.html#cache-dirs">7.3. Cache Directories</a></span></dt><dt><span class="sect2"><a href="optionalfeatures.html#maint-cache">7.4. Maintenance</a></span></dt></dl></dd><dt><span class="sect1"><a href="optionalfeatures.html#exact-address">8. Exact Address Generation</a></span></dt><dt><span class="sect1"><a href="optionalfeatures.html#sending-mixmaster">9. Sending Anonymous Messages via Mixmaster</a></span></dt></dl></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="optionalfeatures-notes"></a>1. General Notes</h2></div></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="compile-time-features"></a>1.1. Enabling/Disabling Features</h3></div></div></div><p> Mutt supports several of optional features which can be enabled or disabled at compile-time by giving the <span class="emphasis"><em>configure</em></span> script certain arguments. These are listed in the <span class="quote">“<span class="quote">Optional features</span>”</span> section of the <span class="emphasis"><em>configure --help</em></span> output. </p><p> Which features are enabled or disabled can later be determined from the output of <code class="literal">mutt -v</code>. If a compile option starts with <span class="quote">“<span class="quote">+</span>”</span> it is enabled and disabled if prefixed with <span class="quote">“<span class="quote">-</span>”</span>. For example, if Mutt was compiled using GnuTLS for encrypted communication instead of OpenSSL, <code class="literal">mutt -v</code> would contain: </p><pre class="screen"> -USE_SSL_OPENSSL +USE_SSL_GNUTLS</pre></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="url-syntax"></a>1.2. URL Syntax</h3></div></div></div><p> Mutt optionally supports the IMAP, POP3 and SMTP protocols which require to access servers using URLs. The canonical syntax for specifying URLs in Mutt is (an item enclosed in <code class="literal">[]</code> means it is optional and may be omitted): </p><pre class="screen"> proto[s]://[username[:password]@]server[:port][/path] </pre><p> <span class="emphasis"><em>proto</em></span> is the communication protocol: <code class="literal">imap</code> for IMAP, <code class="literal">pop</code> for POP3 and <code class="literal">smtp</code> for SMTP. If <span class="quote">“<span class="quote">s</span>”</span> for <span class="quote">“<span class="quote">secure communication</span>”</span> is appended, Mutt will attempt to establish an encrypted communication using SSL or TLS. </p><p> Since all protocols supported by Mutt support/require authentication, login credentials may be specified in the URL. This has the advantage that multiple IMAP, POP3 or SMTP servers may be specified (which isn't possible using, for example, <a class="link" href="reference.html#imap-user" title="3.106. imap_user">$imap_user</a>). The username may contain the <span class="quote">“<span class="quote">@</span>”</span> symbol being used by many mail systems as part of the login name. The special characters <span class="quote">“<span class="quote">/</span>”</span> (<code class="literal">%2F</code>), <span class="quote">“<span class="quote">:</span>”</span> (<code class="literal">%3A</code>) and <span class="quote">“<span class="quote">%</span>”</span> (<code class="literal">%25</code>) have to be URL-encoded in usernames using the <code class="literal">%</code>-notation. </p><p> A password can be given, too but is not recommended if the URL is specified in a configuration file on disk. </p><p> If no port number is given, Mutt will use the system's default for the given protocol (usually consulting <code class="literal">/etc/services</code>). </p><p> The optional path is only relevant for IMAP and ignored elsewhere. </p><div class="example"><a id="ex-url"></a><p class="title"><strong>Example 6.1. URLs</strong></p><div class="example-contents"><pre class="screen"> pops://host/ imaps://user@host/INBOX/Sent smtp://user@host:587/ </pre></div></div><br class="example-break" /></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="ssl"></a>2. SSL/TLS Support</h2></div></div></div><p> If Mutt is compiled with IMAP, POP3 and/or SMTP support, it can also be compiled with support for SSL or TLS using either OpenSSL or GnuTLS ( by running the <span class="emphasis"><em>configure</em></span> script with the <span class="emphasis"><em>--enable-ssl=...</em></span> option for OpenSSL or <span class="emphasis"><em>--enable-gnutls=...</em></span> for GnuTLS). Mutt can then attempt to encrypt communication with remote servers if these protocols are suffixed with <span class="quote">“<span class="quote">s</span>”</span> for <span class="quote">“<span class="quote">secure communication</span>”</span>. </p></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="pop"></a>3. POP3 Support</h2></div></div></div><p> If Mutt is compiled with POP3 support (by running the <span class="emphasis"><em>configure</em></span> script with the <span class="emphasis"><em>--enable-pop</em></span> flag), it has the ability to work with mailboxes located on a remote POP3 server and fetch mail for local browsing. </p><p> Remote POP3 servers can be accessed using URLs with the <code class="literal">pop</code> protocol for unencrypted and <code class="literal">pops</code> for encrypted communication, see <a class="xref" href="optionalfeatures.html#url-syntax" title="1.2. URL Syntax">Section 1.2, “URL Syntax”</a> for details. </p><p> 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 <a class="link" href="reference.html#pop-checkinterval" title="3.183. pop_checkinterval">$pop_checkinterval</a> variable, which defaults to every 60 seconds. </p><p> POP is read-only which doesn't allow for some features like editing messages or changing flags. However, using <a class="xref" href="optionalfeatures.html#header-caching" title="7.1. Header Caching">Section 7.1, “Header Caching”</a> and <a class="xref" href="optionalfeatures.html#body-caching" title="7.2. Body Caching">Section 7.2, “Body Caching”</a> Mutt simulates the new/old/read flags as well as flagged and replied. Mutt applies some logic on top of remote messages but cannot change them so that modifications of flags are lost when messages are downloaded from the POP server (either by Mutt or other tools). </p><a id="fetch-mail"></a><p> Another way to access your POP3 mail is the <code class="literal"><fetch-mail></code> function (default: G). It allows to connect to <a class="link" href="reference.html#pop-host" title="3.185. pop_host">$pop_host</a>, fetch all your new mail and place it in the local <a class="link" href="reference.html#spoolfile" title="3.265. spoolfile">$spoolfile</a>. After this point, Mutt runs exactly as if the mail had always been local. </p><div class="note"><h3 class="title">Note</h3><p> If you only need to fetch all messages to a local mailbox you should consider using a specialized program, such as <code class="literal">fetchmail(1)</code>, <code class="literal">getmail(1)</code> or similar. </p></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="imap"></a>4. IMAP Support</h2></div></div></div><p> If Mutt was compiled with IMAP support (by running the <span class="emphasis"><em>configure</em></span> script with the <span class="emphasis"><em>--enable-imap</em></span> flag), it has the ability to work with folders located on a remote IMAP server. </p><p> You can access the remote inbox by selecting the folder by its URL (see <a class="xref" href="optionalfeatures.html#url-syntax" title="1.2. URL Syntax">Section 1.2, “URL Syntax”</a> for details) using the <code class="literal">imap</code> or <code class="literal">imaps</code> protocol. Alternatively, a pine-compatible notation is also supported, i.e. <code class="literal">{[username@]imapserver[:port][/ssl]}path/to/folder</code> </p><p> Note that not all servers use <span class="quote">“<span class="quote">/</span>”</span> as the hierarchy separator. Mutt should correctly notice which separator is being used by the server and convert paths accordingly. </p><p> 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 <span class="emphasis"><em>toggle-subscribed</em></span> command. See also the <a class="link" href="reference.html#imap-list-subscribed" title="3.99. imap_list_subscribed">$imap_list_subscribed</a> variable. </p><p> Polling for new mail on an IMAP server can cause noticeable delays. So, you'll want to carefully tune the <a class="link" href="reference.html#mail-check" title="3.115. mail_check">$mail_check</a> and <a class="link" href="reference.html#timeout" title="3.287. timeout">$timeout</a> variables. Reasonable values are: </p><pre class="screen"> set mail_check=90 set timeout=15 </pre><p> with relatively good results even over slow modem lines. </p><div class="note"><h3 class="title">Note</h3><p> 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. </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="imap-browser"></a>4.1. The IMAP Folder Browser</h3></div></div></div><p> 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: </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> In lieu of file permissions, Mutt displays the string <span class="quote">“<span class="quote">IMAP</span>”</span>, possibly followed by the symbol <span class="quote">“<span class="quote">+</span>”</span>, indicating that the entry contains both messages and subfolders. On Cyrus-like servers folders will often contain both messages and subfolders. </p></li><li class="listitem"><p> For the case where an entry can contain both messages and subfolders, the selection key (bound to <code class="literal">enter</code> by default) will choose to descend into the subfolder view. If you wish to view the messages in that folder, you must use <code class="literal">view-file</code> instead (bound to <code class="literal">space</code> by default). </p></li><li class="listitem"><p> You can create, delete and rename mailboxes with the <code class="literal"><create-mailbox></code>, <code class="literal"><delete-mailbox></code>, and <code class="literal"><rename-mailbox></code> commands (default bindings: <code class="literal">C</code>, <code class="literal">d</code> and <code class="literal">r</code>, respectively). You may also <code class="literal"><subscribe></code> and <code class="literal"><unsubscribe></code> to mailboxes (normally these are bound to <code class="literal">s</code> and <code class="literal">u</code>, respectively). </p></li></ul></div></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="imap-authentication"></a>4.2. Authentication</h3></div></div></div><p> 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 <span class="quote">“<span class="quote">anonymous</span>”</span>. </p><p> 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 <span class="emphasis"><em>--with-sasl</em></span> flag. </p><p> Mutt will try whichever methods are compiled in and available on the server, in the following order: SASL, ANONYMOUS, GSSAPI, CRAM-MD5, LOGIN. </p><p> There are a few variables which control authentication: </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> <a class="link" href="reference.html#imap-user" title="3.106. imap_user">$imap_user</a> - 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 (i.e. by using a mailbox name of the form <code class="literal">{user@host}</code>). </p></li><li class="listitem"><p> <a class="link" href="reference.html#imap-pass" title="3.101. imap_pass">$imap_pass</a> - a password which you may preset, used by all authentication methods where a password is needed. </p></li><li class="listitem"><p> <a class="link" href="reference.html#imap-authenticators" title="3.93. imap_authenticators">$imap_authenticators</a> - 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). </p></li></ul></div></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="smtp"></a>5. SMTP Support</h2></div></div></div><p> Besides supporting traditional mail delivery through a sendmail-compatible program, Mutt supports delivery through SMTP if it was configured and built with <code class="literal">--enable-smtp</code>. </p><p> If the configuration variable <a class="link" href="reference.html#smtp-url" title="3.258. smtp_url">$smtp_url</a> is set, Mutt will contact the given SMTP server to deliver messages; if it is unset, Mutt will use the program specified by <a class="link" href="reference.html#sendmail" title="3.226. sendmail">$sendmail</a>. </p><p> For details on the URL syntax, please see <a class="xref" href="optionalfeatures.html#url-syntax" title="1.2. URL Syntax">Section 1.2, “URL Syntax”</a>. </p><p> The built-in SMTP support supports encryption (the <code class="literal">smtps</code> protocol using SSL or TLS) as well as SMTP authentication using SASL. The authentication mechanisms for SASL are specified in <a class="link" href="reference.html#smtp-authenticators" title="3.256. smtp_authenticators">$smtp_authenticators</a> defaulting to an empty list which makes Mutt try all available methods from most-secure to least-secure. </p></div><div class="sect1"><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> Usage: </p><div class="cmdsynopsis"><p><code class="command">account-hook</code> <em class="replaceable"><code>pattern</code></em> <em class="replaceable"><code>command</code></em> </p></div><p> If you happen to have accounts on multiple IMAP, POP and/or SMTP servers, you may find managing all the authentication settings inconvenient and error-prone. The <a class="link" href="optionalfeatures.html#account-hook" title="6. Managing Multiple Accounts"><span class="command"><strong>account-hook</strong></span></a> command may help. This hook works like <a class="link" href="configuration.html#folder-hook" title="7. Setting Variables Based Upon Mailbox"><span class="command"><strong>folder-hook</strong></span></a> but is invoked whenever Mutt needs to access a remote mailbox (including inside the folder browser), not just when you open the mailbox. This includes (for example) polling for new mail, storing Fcc messages and saving messages to a folder. As a consequence, <a class="link" href="optionalfeatures.html#account-hook" title="6. Managing Multiple Accounts"><span class="command"><strong>account-hook</strong></span></a> should only be used to set connection-related settings such as passwords or tunnel commands but not settings such as sender address or name (because in general it should be considered unpredictable which <a class="link" href="optionalfeatures.html#account-hook" title="6. Managing Multiple Accounts"><span class="command"><strong>account-hook</strong></span></a> was last used). </p><p> Some examples: </p><pre class="screen"> 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"' account-hook smtp://user@host3/ 'set tunnel="ssh host3 /usr/libexec/smtpd"' </pre><p> To manage multiple accounts with, for example, different values of <a class="link" href="reference.html#record" title="3.207. record">$record</a> or sender addresses, <a class="link" href="configuration.html#folder-hook" title="7. Setting Variables Based Upon Mailbox"><span class="command"><strong>folder-hook</strong></span></a> has to be be used together with the <a class="link" href="configuration.html#mailboxes" title="14. Monitoring Incoming Mail"><span class="command"><strong>mailboxes</strong></span></a> command. </p><div class="example"><a id="ex-multiaccount"></a><p class="title"><strong>Example 6.2. Managing multiple accounts</strong></p><div class="example-contents"><pre class="screen"> mailboxes imap://user@host1/INBOX folder-hook imap://user@host1/ 'set folder=imap://host1/ ; set record=+INBOX/Sent' mailboxes imap://user@host2/INBOX folder-hook imap://user@host2/ 'set folder=imap://host2/ ; set record=+INBOX/Sent' </pre></div></div><br class="example-break" /><p> In example <a class="xref" href="optionalfeatures.html#ex-multiaccount" title="Example 6.2. Managing multiple accounts">Example 6.2, “Managing multiple accounts”</a> the folders are defined using <a class="link" href="configuration.html#mailboxes" title="14. Monitoring Incoming Mail"><span class="command"><strong>mailboxes</strong></span></a> so Mutt polls them for new mail. Each <a class="link" href="configuration.html#folder-hook" title="7. Setting Variables Based Upon Mailbox"><span class="command"><strong>folder-hook</strong></span></a> triggers when one mailbox below each IMAP account is opened and sets <a class="link" href="reference.html#folder" title="3.64. folder">$folder</a> to the account's root folder. Next, it sets <a class="link" href="reference.html#record" title="3.207. record">$record</a> to the <span class="emphasis"><em>INBOX/Sent</em></span> folder below the newly set <a class="link" href="reference.html#folder" title="3.64. folder">$folder</a>. Please notice that the value the <span class="quote">“<span class="quote">+</span>”</span> <a class="link" href="advancedusage.html#shortcuts" title="8. Mailbox Shortcuts">mailbox shortcut</a> refers to depends on the <span class="emphasis"><em>current</em></span> value of <a class="link" href="reference.html#folder" title="3.64. folder">$folder</a> and therefore has to be set separately per account. Setting other values like <a class="link" href="reference.html#from" title="3.73. from">$from</a> or <a class="link" href="reference.html#signature" title="3.231. signature">$signature</a> is analogous to setting <a class="link" href="reference.html#record" title="3.207. record">$record</a>. </p></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="caching"></a>7. Local Caching</h2></div></div></div><p> Mutt contains two types of local caching: <span class="emphasis"><em>(1)</em></span> the so-called <span class="quote">“<span class="quote">header caching</span>”</span> and <span class="emphasis"><em>(2)</em></span> the so-called <span class="quote">“<span class="quote">body caching</span>”</span> which are both described in this section. </p><p> Header caching is optional as it depends on external libraries, body caching is always enabled if Mutt is compiled with POP and/or IMAP support as these use it (body caching requires no external library). </p><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="header-caching"></a>7.1. Header Caching</h3></div></div></div><p> Mutt provides optional support for caching message headers for the following types of folders: IMAP, POP, Maildir and MH. Header caching greatly speeds up opening large folders because for remote folders, headers usually only need to be downloaded once. For Maildir and MH, reading the headers from a single file is much faster than looking at possibly thousands of single files (since Maildir and MH use one file per message.) </p><p> Header caching can be enabled via the configure script and the <span class="emphasis"><em>--enable-hcache</em></span> option. It's not turned on by default because external database libraries are required: one of tokyocabinet, qdbm, gdbm or bdb must be present. </p><p> If enabled, <a class="link" href="reference.html#header-cache" title="3.77. header_cache">$header_cache</a> 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. </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="body-caching"></a>7.2. Body Caching</h3></div></div></div><p> Both cache methods can be combined using the same directory for storage (and for IMAP/POP even provide meaningful file names) which simplifies manual maintenance tasks. </p><p> 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. </p><p> For configuration, the variable <a class="link" href="reference.html#message-cachedir" title="3.130. message_cachedir">$message_cachedir</a> must point to a directory. There, Mutt will create a hierarchy of subdirectories named like the account and mailbox path the cache is for. </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="cache-dirs"></a>7.3. Cache Directories</h3></div></div></div><p> For using both, header and body caching, <a class="link" href="reference.html#header-cache" title="3.77. header_cache">$header_cache</a> and <a class="link" href="reference.html#message-cachedir" title="3.130. message_cachedir">$message_cachedir</a> can be safely set to the same value. </p><p> In a header or body cache directory, Mutt creates a directory hierarchy named like: <code class="literal">proto:user@hostname</code> where <code class="literal">proto</code> is either <span class="quote">“<span class="quote">pop</span>”</span> or <span class="quote">“<span class="quote">imap.</span>”</span> Within there, for each folder, Mutt stores messages in single files and header caches in files with the <span class="quote">“<span class="quote">.hcache</span>”</span> extension. All files can be removed as needed if the consumed disk space becomes an issue as Mutt will silently fetch missing items again. Pathnames are always stored in UTF-8 encoding. </p><p> For Maildir and MH, the header cache files are named after the MD5 checksum of the path. </p></div><div class="sect2"><div class="titlepage"><div><div><h3 class="title"><a id="maint-cache"></a>7.4. Maintenance</h3></div></div></div><p> Mutt does not (yet) support maintenance features for header cache database files so that files have to be removed in case they grow too big. It depends on the database library used for header caching whether disk space freed by removing messages is re-used. </p><p> For body caches, Mutt can keep the local cache in sync with the remote mailbox if the <a class="link" href="reference.html#message-cache-clean" title="3.129. message_cache_clean">$message_cache_clean</a> variable is set. Cleaning means to remove messages from the cache which are no longer present in the mailbox which only happens when other mail clients or instances of Mutt using a different body cache location delete messages (Mutt itself removes deleted messages from the cache when syncing a mailbox). As cleaning can take a noticeable amount of time, it should not be set in general but only occasionally. </p></div></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="exact-address"></a>8. Exact Address Generation</h2></div></div></div><p> Mutt supports the <span class="quote">“<span class="quote">Name <user@host></span>”</span> address syntax for reading and writing messages, the older <span class="quote">“<span class="quote">user@host (Name)</span>”</span> syntax is only supported when reading messages. The <span class="emphasis"><em>--enable-exact-address</em></span> switch can be given to configure to build it with write-support for the latter syntax. <code class="literal">EXACT_ADDRESS</code> in the output of <code class="literal">mutt -v</code> indicates whether it's supported. </p></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="sending-mixmaster"></a>9. Sending Anonymous Messages via Mixmaster</h2></div></div></div><p> You may also have compiled Mutt to co-operate with Mixmaster, an anonymous remailer. Mixmaster permits you to send your messages anonymously using a chain of remailers. Mixmaster support in Mutt is for mixmaster version 2.04 or later. </p><p> To use it, you'll have to obey certain restrictions. Most important, you cannot use the <code class="literal">Cc</code> and <code class="literal">Bcc</code> headers. To tell Mutt to use mixmaster, you have to select a remailer chain, using the mix function on the compose menu. </p><p> The chain selection screen is divided into two parts. In the (larger) upper part, you get a list of remailers you may use. In the lower part, you see the currently selected chain of remailers. </p><p> You can navigate in the chain using the <code class="literal"><chain-prev></code> and <code class="literal"><chain-next></code> functions, which are by default bound to the left and right arrows and to the <code class="literal">h</code> and <code class="literal">l</code> keys (think vi keyboard bindings). To insert a remailer at the current chain position, use the <code class="literal"><insert></code> function. To append a remailer behind the current chain position, use <code class="literal"><select-entry></code> or <code class="literal"><append></code>. You can also delete entries from the chain, using the corresponding function. Finally, to abandon your changes, leave the menu, or <code class="literal"><accept></code> them pressing (by default) the <code class="literal">Return</code> key. </p><p> Note that different remailers do have different capabilities, indicated in the %c entry of the remailer menu lines (see <a class="link" href="">$mix_entry_format</a>). Most important is the <span class="quote">“<span class="quote">middleman</span>”</span> capability, indicated by a capital <span class="quote">“<span class="quote">M</span>”</span>: This means that the remailer in question cannot be used as the final element of a chain, but will only forward messages to other mixmaster remailers. For details on the other capabilities, please have a look at the mixmaster documentation. </p></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="security.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. Security Considerations</td></tr></table></div></body></html>