C.1.1 Results from mu and mu4e differ - why? ¶

In general, the same queries for mu and mu4e should yield the same results. If they differ, this is usually because one of the following reasons:

• Database caching: changes in mu4e are not immediately visible in the command-line mu, since it can take a while before changes are committed to disk (for performance reasons). Note that quitting mu4e or invoking mu4e-update-mail-and-index and mu4e-update-index trigger committing to disk as a side-effect.
• different options: mu4e defaults to having mu4e-headers-include-related, and mu4e-headers-results-limit set to 500. However, the command-line mu find’s corresponding --include-related is false, and there’s no limit (--maxnum). Furthermore, mu find by default includes duplicate messages, while mu4e does not (see --skip-dups/mu4e-search-skip-duplicates.
• reverse sorting: The results may be different when mu4e and mu find do not both sort their results in the same direction.
• shell quoting issues: Depending on the shell, various shell metacharacters in search query (such as *) may be expanded by the shell before mu ever sees them, and the query may not be what you think it is. Quoting is necessary.

C.1.2 The counts in the main-screen differ from the ’real’ numbers - why? ¶

For speed reasons, the counts do not exclude messages that no longer exist in the file-system, nor do they exclude duplicate messages; See mu-mu4e-differ.

C.1.3 How can I quickly delete/move/trash a lot of messages? ¶

You can select (’mark’ in Emacs-speak) messages, just like you would select text in a buffer; the actions you then take (e.g., DEL for delete, m for move and t for trash) apply to all selected messages. You can also use functions like mu4e-headers-mark-thread (T), mu4e-headers-mark-subthread (t) to mark whole threads at the same time, and mu4e-headers-mark-pattern (%) to mark all messages matching a certain regular expression.

Note that when you haven’t enabled separate threads in the headers view, the thread marking functions simply mark all messages.

C.1.4 Can I automatically apply the marks when leaving the headers buffer? ¶

Yes you can — see the documentation for the variable mu4e-headers-leave-behavior.

C.1.5 How can I set mu4e as the default e-mail client in Emacs? ¶

See Default email client.

C.1.6 Can mu4e use some fancy Unicode instead of boring ASCII? ¶

Glad you asked! Yes, if you set mu4e-use-fancy-chars to t, mu4e uses such fancy characters in a number of places. Since not all fonts include all characters, you may want to install the unifont and/or symbola fonts on your system.

C.1.7 Can I start mu4e in the background? ¶

Yes — if you provide a prefix-argument (C-u), mu4e starts, but does not show the main-window.

C.1.8 Does mu4e support searching for CJK (Chinese-Japanese-Korean) characters? ¶

Yes. This is not enabled by default though, since this is fairly intrusive, and influences both indexing and querying. The enable this, pass --support-ngrams to mu init; see the mu-init manpage for further details.

C.1.9 How can I customize the function to select a folder? ¶

The mu4e-completing-read-function variable can be customized to select a folder in any way. The variable can be set to a function that receives five arguments, following completing-read. The default value is ido-completing-read; to use emacs’s default behavior, set the variable to completing-read. Helm users can use the same value, and by enabling helm-mode use helm-style completion.

C.1.10 With a lot of Maildir folders, jumping to them can get slow. What can I do? ¶

Set mu4e-cache-maildir-list to t (make sure to read its docstring).

C.1.11 How can I hide certain messages from the search results? ¶

See the variables mu4e-headers-hide-predicate and mu4e-headers-hide-enabled. The latter can be toggled through mu4e-search-toggle-property.

For example, to filter out GMail’s spam folder, set it to:

(setq mu4e-headers-hide-predicate
     (lambda (msg)
       (string-suffix-p "Spam" (mu4e-message-field msg :maildir))))

C.1.12 I’m getting ’Variable binding depth exceeds...’. What can I do about it? ¶

The error 'Variable binding depth exceeds max-specpdl-size' occurs because mu4e is binding more variables than emacs allows for, by default. You can avoid this by setting a higher value, e.g. by adding the following to your configuration:

(setq max-specpdl-size 5000)

Note that Emacs 29 obsoletes this variable.