feedmail-queue-run-orderer

feedmail-queue-run-orderer is a variable defined in `feedmail.el'.
Its value is

nil

Documentation:
If non-nil, name a function which will sort the queued messages.
The function is called during a running of the queue for sending, and
takes one argument, a list of the files in the queue directory. It
may contain the names of non-message files, and it's okay to leave
them in the list when reordering it; they get skipped over later.
When nil, the default action processes the messages in normal sort
order by queued file name, which will typically result in the order
they were placed in the queue.

You can customize this variable.