[mdlug] Quotas. How do they work?

[Adam Tauno Williams]

On Tue, 2011-03-29 at 10:42 -0400, Mark Montague wrote:
> On March 29, 2011 10:16 , "Robert Adkins II" <radkins at impelind.com> wrote:
> > I am seeking to force certain users into trimming back the size of their
> > email stored on the IMAP server. Much of the data itself doesn't need to be
> > stored in email long term, as it is replicated elsewhere on the network.
> > The problem is, if I just toss in a quota I am concerned that there will be
> > no warning, just suddenly they will be unable to send/receive email. Nothing
> > I am seeing the in the tools for enabling quotas suggests that the users
> > will receive any form of warning.
> > Is this true?
> Are you sure you want to impose quotas?  At the University of Michigan 
> (for example), adding another drive to an IMAP server's RAID array (or 
> upgrading the drives to higher capacity ones, if possible) is cheaper 
> than imposing and managing quotas, and then paying for the resulting end 
> user support.  Plenty of people have 5 GB, 10 GB, even 20 GB mailboxes, 
> and the very rare problem cases can usually be addressed by having a 
> chat with the offending user.  (If this sounds radical, keep in mind 
> that as of today, Google is providing 7.6 GB per user at no cost, with 
> extra space available very cheaply).

I think there is a real organizational value to making people delete
junk; but that is another argument entirely.

> - Use IMAP quotas rather than Unix filesystem quotas, if at all 
> possible.  This will give you much more "intelligence", nicer failure 
> modes, and hopefully better control.

Every client I've seen (Thunderbird, Evolution, Horde) reports IMAP
quota status.  Horde very prominantly, Evolution you have to check,
Thunderbird starts to whine at ~80%.

> - Configure your SMTP / LMTP server to hold messages for up to 7 days if 
> they cannot be delivered due to a mailbox being over quota.  

+1

> - Provide a web interface where people can check their current quota usage.

You might discover that whatever you currently use does that
automatically as soon as you turn IMAP quotas on.

> - Keep in mind that if the user uses a client that uses a Trash folder, 
> this can sometimes complicate things.  See the question "Why can't I 
> delete any messages from my over-quota mailbox?" at 
> http://www.cyrusimap.org/docs/cyrus-imapd/2.4.6/faq.php

Yes, Trash is an evil and stupid concept.  That is really the only one
that gives us grief.  But you can set Cyrus to auto-expire messages in a
folder, which works well [if you are using Cyrus].