If you want to change some setting, or execute some custom action before
message composition starts, you can define a hook function. mu4e
offers two hooks:
mu4e-compose-pre-hook: this hook is run before composition
starts; if you are composing a reply, forward a message, or
edit an existing message, the variable
mu4e-compose-parent-message points to the message being replied to,
forwarded or edited, and you can use mu4e-message-field to get the
value of various properties (and see Message functions).
mu4e-compose-mode-hook: this hook is run just before composition
starts, when the whole buffer has already been set up. This is a good place
for editing-related settings. mu4e-compose-parent-message (see above)
is also at your disposal.
mu4e-compose-post-hook: this hook is run when we’re done with
message compositions. See the docstring for details.
As mentioned, mu4e-compose-mode-hook is especially useful for
editing-related settings:
Let’s look at an example:
(add-hook 'mu4e-compose-mode-hook
(defun my-do-compose-stuff ()
"My settings for message composition."
(set-fill-column 72)
(flyspell-mode)))
The hook is also useful for adding headers or changing headers, since the
message is fully formed when this hook runs. For example, to add a
Bcc:-header, you could add something like the following, using
message-add-header from message-mode.
(add-hook 'mu4e-compose-mode-hook
(defun my-add-bcc ()
"Add a Bcc: header."
(save-excursion (message-add-header "Bcc: me@example.com\n"))))
Or to something context-specific:
(add-hook 'mu4e-compose-mode-hook
(lambda()
(let* ((ctx (mu4e-context-current))
(name (if ctx (mu4e-context-name ctx))))
(when name
(cond
((string= name "account1")
(save-excursion (message-add-header "Bcc: account1@example.com\n")))
((string= name "account2")
(save-excursion (message-add-header "Bcc: account2@example.com\n"))))))))
For a more general discussion about extending mu4e, see Extending mu4e.