[imp] Can I enable "Quota" function with my imap server ?

[Eric Rostetter]

Quoting Ken Weaverling <weave@hopi.dtcc.edu>:

> The imap server that comes with Redhat is uw-imap, which doesn't support imap
> quotas and doesn't work well with hard disk quotas.

Depends.  Many people put quotas on the home directories, but not on the
/var/spool/mail partition.  Then they use the mbox driver to automatically
move the mail from /var/spool/mail to the user's home directory.  This works
well.

> If your mail server sits on a box where users have access to store files via
> other non-imap means (example, via shell access or samba), then quotas become
> more problematic.

Correct.

> Redhat supports disk quotas but that introduces another problem, in that imap
> won't report what the usage is.

Correct.  See https://mail.ph.utexas.edu/patches/wu-imap-quotas/ for some
background.

> Even if it did, file system quotas present
> numerous problems for the imap client user.

If done via mbox driver in home directories, then it presents no more 
problems than quotas in general present.

> For example, if you hit your quota
> limit, your first reaction is to delete messages. But once you delete, it
> either
> moves the message to Trash (which fails, no space) or expunge it (which fails
> since it copies the folder without deleted messages, and then deletes
> original folder).

Yep.  Can be reduced by using soft/hard quotas, but can't be avoided.
I think maybe CVS HEAD might get around this if using the "empty folder"
option, but even if it does, that would require nuking the entire folder
which often isn't desirable. :)

> With all that in mind, I'm trying to think of a best way around this. Since
> my
> horde server, imap server, and disk storage is all on one system, I don't
> need
> to use imap to find a quota. So I was hoping to write an imp quota hook that
> queried the file system quota for the user, then subtract some margin of
> safety,
> then report that usage.  I was thinking more like 50% less than disk quota.

Been doing this for RH6.x and RH8.x for years now.  But without the margin,
instead use hard/soft quotas for the margin.

> Still doesn't solve all the issues though. So you report 100% used, but it's
> really 50% to allow for stuff to be shuffled around to get deleted. Then
> what?

See hard/soft quota limits.

> People could ignore it, so there has to be a way to force user to manage
> quota.

True.  People ignore the quotas until it causes a problem (like they can't
login).  No way around that.

> Possibilities include hook into the send message routine and deny sending
> until
> under quota, or force maintenance on logon to get messages down, etc, etc...

I don't think I would really want to resort to anything like that personally,
though an annoying message at login would be of interest...

> Not an easy issue! If you have a closed-box imap/mail system, it would
> probably
> be easier to switch to courier imap.

Maybe, but maybe not.  There are other issues here.

> The father of imap and author of uw-imap, Mark Crispin, has a lot to say
> about
> this issue. Just use groups.google.com to search the comp.mail.imap group for
> his name and the keyword quota and you should find those arguments easily!

Probably good advice.

-- 
Eric Rostetter
The Department of Physics
The University of Texas at Austin

Why get even? Get odd!