Agent Commands Gnus Unplugged Outgoing Messages
nnagent doesn't handle expiry. Instead, there's a special
gnus-agent-expire command that will expire all read articles that
are older than
gnus-agent-expire-days days. It can be run
whenever you feel that you're running out of space. It's not
particularly fast or efficient, and it's not a particularly good idea to
interrupt it (with C-g or anything else) once you've started it.
gnus-agent-expire-all is non-
nil, this command will
expire all articles---unread, read, ticked and dormant. If
(which is the default), only read articles are eligible for expiry, and
unread, ticked and dormant articles will be kept indefinitely.