[Dovecot] making IMAP quicker on LAN

[Jack Stewart]

Ed W wrote:
> 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

A few IMAP client based things that seem to help are: disable all of the 
languages you don't need in Thunderbird; configure AppleMail to download 
only the messages you've read; configure Outlook/Outlook Express to sync 
at a more reasonable level to limit it from downloading everything every 
time; or make everyone use mutt/pine. The last isn't realistic but if 
mutt or pine works fine, then you know some client optimizations will help.

Webmail, as long as it isn't loaded with too much graphics, might work 
better with slow connections. For people connecting to Email while in a 
Rain Forest, POP seems to be the best option.

It also seems to me that fts plugin (free text indexing) improves 
performance. This might just be wishful thinking on my part.

Hope this helps a little.

---Jack