The index is the screen that you usually see first when you start Mutt. It gives an overview over your emails in the currently opened mailbox. By default, this is your system mailbox. The information you see in the index is a list of emails, each with its number on the left, its flags (new email, important email, email that has been forwarded or replied to, tagged email, ...), the date when email was sent, its sender, the email size, and the subject. Additionally, the index also shows thread hierarchies: when you reply to an email, and the other person replies back, you can see the other person's email in a "sub-tree" below. This is especially useful for personal email between a group of people or when you've subscribed to mailing lists.

The pager is responsible for showing the email content. On the top of the pager you have an overview over the most important email headers like the sender, the recipient, the subject, and much more information. How much information you actually see depends on your configuration, which we'll describe below.

Below the headers, you see the email body which usually contains the message. If the email contains any attachments, you will see more information about them below the email body, or, if the attachments are text files, you can view them directly in the pager.

To give the user a good overview, it is possible to configure Mutt to show different things in the pager with different colors. Virtually everything that can be described with a regular expression can be colored, e.g. URLs, email addresses or smileys.

The file browser is the interface to the local or remote file system. When selecting a mailbox to open, the browser allows custom sorting of items, limiting the items shown by a regular expression and a freely adjustable format of what to display in which way. It also allows for easy navigation through the file system when selecting file(s) to attach to a message, select multiple files to attach and many more.

The help screen is meant to offer a quick help to the user. It lists the current configuration of key bindings and their associated commands including a short description, and currently unbound functions that still need to be associated with a key binding (or alternatively, they can be called via the Mutt command prompt).

The compose menu features a split screen containing the information which really matter before actually sending a message by mail: who gets the message as what (recipients and who gets what kind of copy). Additionally, users may set security options like deciding whether to sign, encrypt or sign and encrypt a message with/for what keys. Also, it's used to attach messages, to re-edit any attachment including the message itself.

The alias menu is used to help users finding the recipients of messages. For users who need to contact many people, there's no need to remember addresses or names completely because it allows for searching, too. The alias mechanism and thus the alias menu also features grouping several addresses by a shorter nickname, the actual alias, so that users don't have to select each single recipient manually.

As will be later discussed in detail, Mutt features a good and stable MIME implementation, that is, it supports sending and receiving messages of arbitrary MIME types. The attachment menu displays a message's structure in detail: what content parts are attached to which parent part (which gives a true tree structure), which type is of what type and what size. Single parts may saved, deleted or modified to offer great and easy access to message's internals.

Mutt has a built-in line editor for inputting text, e.g. email addresses or filenames. The keys used to manipulate text input are very similar to those of Emacs. See Table 2.3, “Most common line editor keys” for a full reference of available functions, their default key bindings, and short descriptions.

You can remap the editor functions using the bind command. For example, to make the <Delete> key delete the character in front of the cursor rather than under, you could use:

bind editor <delete> backspace

Mutt maintains a history for the built-in editor. The number of items is controlled by the $history variable and can be made persistent using an external file specified using $history_file. You may cycle through them at an editor prompt by using the <history-up> and/or <history-down> commands. But notice that Mutt does not remember the currently entered text, it only cycles through history and wraps around at the end or beginning.

Mutt maintains several distinct history lists, one for each of the following categories:

Mutt automatically filters out consecutively repeated items from the history. It also mimics the behavior of some shells by ignoring items starting with a space. The latter feature can be useful in macros to not clobber the history's valuable entries with unwanted entries.

Common keys used to navigate through and manage messages in the index are shown in Table 2.4, “Most common message index keys”. How messages are presented in the index menu can be customized using the $index_format variable.

In addition to who sent the message and the subject, a short summary of the disposition of each message is printed beside the message number. Zero or more of the “flags” in Table 2.5, “Message status flags” may appear, some of which can be turned on or off using these functions: <set-flag> and <clear-flag> bound by default to “w” and “W” respectively.

Furthermore, the flags in Table 2.6, “Message recipient flags” reflect who the message is addressed to. They can be customized with the $to_chars variable.

By default, Mutt uses its built-in pager to display the contents of messages (an external pager such as less(1) can be configured, see $pager variable). The pager is very similar to the Unix program less(1) though not nearly as featureful.

In addition to key bindings in Table 2.7, “Most common pager keys”, many of the functions from the index menu are also available in the pager, such as <delete-message> or <copy-message> (this is one advantage over using an external pager to view messages).

Also, the internal pager supports a couple other advanced features. For one, it will accept and translate the “standard” nroff sequences for bold and underline. These sequences are a series of either the letter, backspace (“^H”), the letter again for bold or the letter, backspace, “_” for denoting underline. Mutt will attempt to display these in bold and underline respectively if your terminal supports them. If not, you can use the bold and underline color objects to specify a color or mono attribute for them.

Additionally, the internal pager supports the ANSI escape sequences for character attributes. Mutt translates them into the correct color and character settings. The sequences Mutt supports are:

\e[Ps;Ps;..Ps;m

where Ps can be one of the codes shown in Table 2.8, “ANSI escape sequences”.

Mutt uses these attributes for handling text/enriched messages, and they can also be used by an external autoview script for highlighting purposes.

So-called “threads” provide a hierarchy of messages where replies are linked to their parent message(s). This organizational form is extremely useful in mailing lists where different parts of the discussion diverge. Mutt displays threads as a tree structure.

In Mutt, when a mailbox is sorted by threads, there are a few additional functions available in the index and pager modes as shown in Table 2.10, “Most common thread mode keys”.

Collapsing a thread displays only the first message in the thread and hides the others. This is useful when threads contain so many messages that you can only see a handful of threads on the screen. See %M in $index_format. For example, you could use “%?M?(#%03M)&(%4l)?” in $index_format to optionally display the number of hidden messages if the thread is collapsed. The %?<char>?<if-part>&<else-part>? syntax is explained in detail in format string conditionals.

Technically, every reply should contain a list of its parent messages in the thread tree, but not all do. In these cases, Mutt groups them by subject which can be controlled using the $strict_threads variable.

In addition, the index and pager menus have these interesting functions:

The bindings shown in Table 2.11, “Most common mail sending keys” are available in the index and pager to start a new message.

Bouncing a message sends the message as-is to the recipient you specify. Forwarding a message allows you to add comments or modify the message you are forwarding. These items are discussed in greater detail in the next section “Forwarding and Bouncing Mail.”

Mutt will then enter the compose menu and prompt you for the recipients to place on the “To:” header field when you hit m to start a new message. Next, it will ask you for the “Subject:” field for the message, providing a default if you are replying to or forwarding a message. You again have the chance to adjust recipients, subject, and security settings right before actually sending the message. See also $askcc, $askbcc, $autoedit, $bounce, $fast_reply, and $include for changing how and if Mutt asks these questions.

When replying, Mutt fills these fields with proper values depending on the reply type. The types of replying supported are:

After getting recipients for new messages, forwards or replies, Mutt will then automatically start your $editor on the message body. If the $edit_headers variable is set, the headers will be at the top of the message in your editor. Any messages you are replying to will be added in sort order to the message, with appropriate $attribution, $indent_string and $post_indent_string. When forwarding a message, if the $mime_forward variable is unset, a copy of the forwarded message will be included. If you have specified a $signature, it will be appended to the message.

Once you have finished editing the body of your mail message, you are returned to the compose menu providing the functions shown in Table 2.12, “Most common compose menu keys” to modify, send or postpone the message.

The compose menu is also used to edit the attachments for a message which can be either files or other messages. The <attach-message> function to will prompt you for a folder to attach messages from. You can now tag messages in that folder and they will be attached to the message you are sending.

When editing the header because of $edit_headers being set, there are a several pseudo headers available which will not be included in sent messages but trigger special Mutt behavior.

If you have told Mutt to PGP or S/MIME encrypt a message, it will guide you through a key selection process when you try to send the message. Mutt will not ask you any questions about keys which have a certified user ID matching one of the message recipients' mail addresses. However, there may be situations in which there are several keys, weakly certified user ID fields, or where no matching keys can be found.

In these cases, you are dropped into a menu with a list of keys from which you can select one. When you quit this menu, or Mutt can't find any matching keys, you are prompted for a user ID. You can, as usually, abort this prompt using ^G. When you do so, Mutt will return to the compose screen.

Once you have successfully finished the key selection, the message will be encrypted using the selected public keys when sent out.

Most fields of the entries in the key selection menu (see also $pgp_entry_format) have obvious meanings. But some explanations on the capabilities, flags, and validity fields are in order.

The flags sequence (“%f”) will expand to one of the flags in Table 2.13, “PGP key menu flags”.

The capabilities field (“%c”) expands to a two-character sequence representing a key's capabilities. The first character gives the key's encryption capabilities: A minus sign (“-”) means that the key cannot be used for encryption. A dot (“.”) means that it's marked as a signature key in one of the user IDs, but may also be used for encryption. The letter “e” indicates that this key can be used for encryption.

The second character indicates the key's signing capabilities. Once again, a “-” implies “not for signing”, “.” implies that the key is marked as an encryption key in one of the user-ids, and “s” denotes a key which can be used for signing.

Finally, the validity field (“%t”) indicates how well-certified a user-id is. A question mark (“?”) indicates undefined validity, a minus character (“-”) marks an untrusted association, a space character means a partially trusted association, and a plus character (“+”) indicates complete validity.