[Dovecot] making IMAP quicker on LAN

[Ed W]

Andrew Von Cid wrote:
> Hi all,
>
> I keep on hitting this problem when migrating new clients from POP or 
> local IMAP servers (hosted on their LAN's) to my Dovecot setup, which 
> is hosted properly in a data center.  People usually complain that 
> it's slower and although they're getting a kick ass mail setup it 
> doesn't look good from their point of view.
>
> I'm wondering if there is anything I could do to speed it up on their 
> LAN's.  What I mean is probably a caching IMAP proxy or some sort of 
> replication to a local Dovecot server.  Is this something Dovecot can 
> do?  I'd be really grateful for any opinions on how to tackle this 
> problem.

My experience is that most mail clients drag down a LOT of data when you 
open a folder, hence the bandwidth required is surprisingly large.  I 
also noticed that this data compresses EXTREMELY well.  So my company 
just happens to make a compression proxy for use on seriously slow 
dialup links (2.4Kbit), but my own experience is that this speeds things 
up by around a factor of 2 on a typical fast broadband link (compared 
using Thunderbird)

There are various simple ways to test this thesis on your own setup, 
including a simple straight through proxy in about 20 lines or perl.  
However, not sure what the best fix is for this problem?

There was some discussion a few weeks back that SSL can have a 
compression layer turned on - Timo pointed out that this was disabled in 
both Dovecot and also TB.  It might be possible to send Timo some money 
and have it enabled in Dovecot (looked like a very trivial one line 
fix?) - you could then (fix and) use ssltunnel to get the benefit whilst 
waiting for your patch to TB to be accepted into mainstream (or if it 
suits your userbase you could fix the code and distribute a changed 
version locally? If using Outlook then obviously this isn't possible, 
but no idea if Outlook already supports compressed SSL?)

You could also pay Timo to add support for the compressed IMAP protocol 
extension, but again you run into the problem that few/no clients 
support it (at least you have half the problem licked though)

Timo is also working on a very clever multi-master imap server 
replication engine - again probably tipping a few euros his way might 
speed up that process.  This would give you a local cache server

Hope those ideas get you started?

Good luck

Ed W