nnimap does not create non-existent groups on expiry (lost mail)

[Nevin Kapur <nevin@jhu.edu>]

I recently moved from using nnfolder groups as expiry targets to using
nnimap groups.  In either case an expiry target that depends on the
message's month and year is being used.  When I was using nnfolder
groups as expiry targets, non-existent groups were being automatically
created.  However this is not the case with nnimap groups.  For
example, I set nnmail-expiry-target to "nnimap:mail/ne", a group that
does not exist, and set about expiring some mail.  To my horror I
discovered that the messages were expired and the new group was not
created, resulting in lost mail.

Here's an excerpt from the imap log: the group is not created and Gnus
is silently losing mail.

3510 UID COPY 7 "mail/ne"
* OK [TRYCREATE] Must create mailbox before copy
3510 NO [TRYCREATE] UID COPY failed: No such destination mailbox

Any fixes?

-Nevin