Function: feedmail-queue-reminder

Perform some kind of reminder activity about queued and draft messages.
Called with an optional symbol argument which says what kind of event
is triggering the reminder activity. The default is 'on-demand, which
is what you typically would use if you were putting this in your Emacs start-up
or mail hook code. Other recognized values for WHAT-EVENT (these are passed
internally by feedmail):

after-immediate (a message has just been sent in immediate mode)
after-queue (a message has just been queued)
after-draft (a message has just been placed in the draft directory)
after-run (the queue has just been run, possibly sending messages)

WHAT-EVENT is used as a key into the table `feedmail-queue-reminder-alist'. If
the associated value is a function, it is called without arguments and is expected
to perform the reminder activity. You can supply your own reminder functions
by redefining `feedmail-queue-reminder-alist'. If you don't want any reminders,
you can set `feedmail-queue-reminder-alist' to nil. (fn &optional WHAT-EVENT)