E.1 High-level overview ¶

At a high level, we can summarize the structure of the mu4e system using some ascii-art:

              +---------+
              | emacs   |
              |    +------+
              +----| mu4e | --> send mail (smtpmail)
                   +------+
                    |  A
                    V  |  ---/ search, view, move mail
              +---------+    \
              |   mu    |
              +---------+
                |    A
                V    |
              +---------+
              | Maildir |  <--- receive mail (fetchmail,
              +---------+                     offlineimap, ...)

In words:

• Your e-mail messages are stored in a Maildir-directory (typically, ~/Maildir and its subdirectories), and new mail comes in using tools like fetchmail, offlineimap, or through a local mail server.
• mu indexes these messages periodically, so you can quickly search for them. mu can run in a special server-mode, where it provides services to client software.
• mu4e, which runs inside Emacs is such a client; it communicates with mu (in its server-mode) to search for messages, and manipulate them.
• mu4e uses the facilities offered by Emacs (the Gnus message editor and smtpmail) to send messages.