Find bogus groups and delete them
(gnus-group-check-bogus-groups).
Find new groups and process them (gnus-group-find-new-groups).
With 1 C-u, use the ask-server method to query the server
for new groups. With 2 C-u’s, use most complete method possible
to query the server for new groups, and subscribe the new groups as
zombies.
Run all expirable articles in the current group through the expiry
process (if any) (gnus-group-expire-articles). That is, delete
all expirable articles in the group that have been around for a while.
(see Expiring Mail).
Run all expirable articles in all groups through the expiry process
(gnus-group-expire-all-groups).