[Dovecot] Advice for new dovecot / imap proxy? setup

[Gedalya]

On 03/23/2012 02:12 PM, Luca Lesinigo wrote:
> Il giorno 23/mar/2012, alle ore 11:50, Timo Sirainen ha scritto:
>> Are you thinking about actual "dummy" proxying (which is normally what Dovecot proxying is about) or about the "imapc" backend (http://www.dovecot.fi/products/105-dovecot-imap-adaptor.html)? If you're using Dovecot as backend servers, there's really no reason to use imapc proxying.
> I actually didn't know about the two different modes. I guess I would need imapc to support the older Courier-IMAP server until I migrated everything away from it, and that I could use "dummy" proxying for the newer dovecot backends.
> I don't know if the two can be used at the same time (eg. imapc to the older backend and dummy to the newer) and/or if there is any drawback in running everything on imapc (old and new dovecot server). I'll be investigating this....
I'm using the dummy proxying with a very different backend, certainly 
not dovecot, and it works great. For your needs (as I understand them) 
It's a much simpler and robust solution than imapc. Try it out. The main 
potential source of trouble is possible differences in the CAPABILITY 
string, but it hasn't caused me any actual problems.

>>> We'd like to support all the recent IMAP goodies to make modern users happy (IMAP IDLE, LEMONADE, etc)
>> Dovecot doesn't support the full LEMONADE yet, but I don't know if there are any LEMONADE clients either.
> Oh well I included it in the list because I read about it somewhere, possibly on the dovecot site. But what I really meant was simply "support the latest goodies" :)
>
> Il giorno 23/mar/2012, alle ore 11:38, Miguel Tormo ha scritto:
>>> - isolate the mailbox servers from direct external access and just run IMAP on them, let other systems run ssl, pop3, smtp, webmail, etc...
>> I don't think I understand you here. You will need to run POP3 on the mailbox servers if you want to give POP3 access to the mailboxes.
> Don't ask me why, but I was thinking that a dovecot proxy could talk just imap to the backends and use that to serve both POP3 and IMAP to clients. And it's possibly what happens with the imapc backend, but I need to do some RTFM about it.

The same proxy_maybe (dummy proxy) setup works great for POP3 too. Very 
simple to set up, works like a charm. Nothing much to think about.

>
>> However, I can confirm you that IMAP IDLE does work with imap proxy.
> That's great, I really want to provide the best possible "push-like" experience to modern clients, and as far as I know IMAP IDLE on the protocol side plus some notification mechanism (as opposed to regular polling) on the backend side is the way to go.

It will work as well as it was working with your existing courier 
server. But it will work great for accounts migrated to native dovecot.

>> You have my comments above, I think it is doable. In my opinion, the IMAP proxy part is the easiest one. MTA configuration to distribute the mails among the different mailbox servers can be trickier.
> Actually that part is already there. Mail enters my systems via some MX servers (with the usual antispam and so on) and it's finally delivered via SMTP to the correct mail server via postfix recipient maps (that's because I already receive on my MXes mail for domains not hosted on my mail server, the common scenario is where I route a domain's mail to the customer's exchange server). But right now the mail server also receives direct SMTP connections from the clients in addition to incoming mail from my MXes and I'd really prefer to separate the two things.

It's a very good idea to have completely separate machines for outgoing 
mail. Once you have imap-only boxes, you can eliminate the need for an 
MTA by using the dovecot LMTP server. Your postfix transport map can 
send mail to either smtp:imap.yourdomain.com:25 or 
lmtp:imap.yourdomain.com:2525 on a per account basis, and you can get 
rid of the MTA in due time.


>> You could use dovecot LMTP proxy and make the MTA deliver mails through LMTP, thus the dovecot proxy instance will handle the sharding for delivering and for reading mail.
> On the proxy system I plan to run postfix to implement authenticated SMTP (it would authenticate on dovecot) and pop/imap-before-smtp (yes we still need to support that :| ), but all mail will be reinjected through our MX servers to be scanned before final delivery (either local or external).

Since you're sending everything back to the MX, you might as well have 
your MX use LMTP, looking up the correct protocol and host from the 
database, and spend the next couple of years telling your customers to 
change their mail client configuration to use a dedicated outgoing mail 
server. It's worth the trouble.

>
> Thanks people for the suggestions, my next stop is getting to know imapc and its details, and how the various other parts will fit with that (eg. giving pop3 service to clients).
>
> --
> Luca Lesinigo