[Dovecot] How to run Dovecot as IMAP Proxy?

[Justin Krejci]

You can also use pimpstat to monitor the effectiveness of imapproxy. We had
imapproxy running running in front of squirrelmail for a post.office IMAP
server (based on uw-imap). We eventually went into the code for imapproxy
and tweaked some of the SELECT caching and even tweaked some of the
squirrelmail imap code a bit to be more efficient with the proxy.

Now we are using Dovecot without imapproxy in front of squirrelmail and
there are no problems.

-----Original Message-----
From: dovecot-bounces+jkrejci=usinternet.com at dovecot.org
[mailto:dovecot-bounces+jkrejci=usinternet.com at dovecot.org] On Behalf Of
Seth Mattinen
Sent: Thursday, May 21, 2009 4:36 PM
To: V S Rao
Cc: Dovecot Mailing List
Subject: Re: [Dovecot] How to run Dovecot as IMAP Proxy?

V S Rao wrote:
> Thanks for the many responses and views.
> 
> I have taken RH support for my mail server only and so have to ensure they
support me. So am going with their recommended version which is 0.99.x.
> 
> Now on the webmail I have migrated to RHEL 5.3 and the dovecot being used
there is 1.0.7.x. So that should support proxying, right? 
> 
> BTW, originally I did not go to Redhat. I moved from uw-imap to Dovecot
1.1.14 on the mail server for POP3. The problem of POP3 timeouts continued
and I could not find any reason why POP3 was timing out when 400+ concurrent
IMAP sessions were working fine. Moreover other network services such as
SMTP, Telnet, SSH etc were working fine. Had the box installed behind a IPS
box to see if there were any DoS attacks, but had to rule that out. As a
last resort, paid RH for support and they made me downgrade Dovecot from
1.1.14 to 0.99.x. Surprisingly the moment I downgraded dovecot, the problem
shifted to IMAP & remained ever since. So naturally they told me uw-imap was
the problem and made me move to Dovecot 0.99.x for IMAP as well, but no
improvement. 
> 
> But the surprising thing, as I mentioned in my original post, IMAP works
fine on command line, with clients such as Outlook, THunderbird etc., but
Webmail is very slow that its almost not available. 
> 
> BTW webmail was also running on RHEL 4.0. Seeing that the problem existed
in webmail alone I upgraded webmail to RHEL 5.3 with all the latest RH
supported packages on a new hardware. 
> 
> Any ideas to help me debug this issue would be of great help as I am stuck
on this issue for almost a month now. 
> 
> Oh, btw regarding stats, I don't have a measure, but when webmail was
working the login was well within 5 seconds. Now it takes forever (more than
a min) or timeouts most of the time. Even after login, any request such as
opening a mail or changing to a mail folder was well within 5 seconds. Now
again it takes forever or timeouts most of the time. 
> 

Use imapproxyd (UP-ImapProxy) if you want a caching proxy for webmail.
It specifically deals with the "webmail constantly logging in" issue.
>From the Debian man page:

"ImapProxy was written to compensate for webmail clients that are unable
 to maintain persistent connections  to an IMAP server. Most webmail
clients need to log in to an IMAP server for nearly every single
transaction; This behaviour can cause tragic performance problems on the
IMAP server.  ImapProxy tries to deal with this  problem by  leaving
server  connections open for a short time after a webmail client logs
out. When the webmail client connects again, ImapProxy will determine if
there is a cached connection available and reuse it if possible."

Dovecot proxy quite simply won't do what it looks like you want to do,
and is irrelevant on your webmail server.

~Seth