Does anyone allow unlimited or extremely large quotas?

Shuvam Misra shuvam.misra at
Tue Nov 16 10:11:46 EST 2010

> > I think the issue you will encounter first is clients will start to fall
> > down when folders exceed a 'reasonable' number of messages.  Common IMAP
> > clients I've seen start to exhibit severe performance issues beyond a
> > few hundred thousand messages.
> As far as I'm aware (the helpdesk guys know better than me so I'm parroting
> their reply), Outlook 2003's PST file has a limit of 2GB so if it's locally
> caching folders, you may run into that.
> If you use Outlook 2007 or later, the limit is more like 20GB.  BUT, if you
> upgrade from 2003 and use the same PST, that PST may continue with the same
> 2GB limit.  Apparently you might need to create a new PST file and move the
> mail into it?.  Some big users have been moved to Thunderbird to avoid this
> and to improve performance.
> Gavin
> ? To be honest, I haven't personally dealt with this issue, but this
>   paraphrases the knowledge of those here who have.  I'd think of it as
>   having "[citation required]" beside it.

I'm in an almost-identical position w.r.t. lack of direct knowledge, but
our Support guys say exactly the same things about Outlook 2003 and
Outlook 2007 and size limits of PST files.

That said, we have users of our product who have 40GB mailboxes.
Cyrus works perfectly happily with all this. The problem is the number
of messages in the current folder, as many have mentioned before me. We
keep telling users to clean up their Inboxes and keep a max of 1,000
msgs there. We know things will be fine with 10,000 messages too, but
100,000 msgs in a folder is pushing things.

We find that Webmail chokes server performance much earlier than normal
IMAP clients do. I know this has nothing to do with Cyrus, but I just
thought I'd mention it. Most programming environments in which such
Webmail thingies are written (mostly PHP on the server and nowadays
lots of Javascript on the browser) cannot keep an IMAP connection to the
Cyrus server open between pages, therefore each time a user clicks on a
folder or does any other operation, there's this fresh IMAP connection
and a huge surge of IMAP operations while the folder contents are listed
afresh, etc. This puts a lot of load on the server. I guess Webmail is
OT on a Cyrus mailing list, but can't help asking: any suggestions for
improving Webmail performance? (Admission: we haven't yet tried imapproxy
-- it appears to be a good piece of C which will help things.)


More information about the Info-cyrus mailing list