feedmail-queue-fqm-suffix

feedmail-queue-fqm-suffix is a variable defined in `feedmail.el'.
Its value is

".fqm"

Documentation:
The FQM suffix used to distinguish feedmail queued message files.
You probably want this to be a period followed by some letters and/or
digits. The distinction is to be able to tell them from other random
files that happen to be in the `feedmail-queue-directory' or
`feedmail-queue-draft-directory'. By the way, FQM stands for feedmail
queued message.

You can customize this variable.