[Dovecot] limit number of simultaneous lmtp deliveries ?

[Timo Sirainen]

On Mon, 2011-09-05 at 11:05 +0200, Jan-Frode Myklebust wrote:
> We have quite a few frontend mail gateways that deliver incoming
> email trough our dovecot director (lmtp proxy) to the backend lmtp
> servers, and are seeing this logged on the frontend mail gateways:
> 
> 	Sep  5 10:51:56 mailgw1 postfix/lmtp[23443]: 0E2F41C01A: to=<me at example.com>, relay=loadbalancers.example.com[192.168.42.15]:24, delay=61, delays=0.02/0.3/31/30, dsn=4.4.0, status=deferred (host loadbalancers.example.com[192.168.42.15] said: 451 4.4.0 Remote server not answering (DATA output timeout) (in reply to end of DATA command))
> 
> It's a bit unclear to me if this leads to duplicate deliveries, or just
> delayed deliveries, 

Possibly randomly either one. I'll need to start looking into these LMTP
proxy bugs some day.. Although for 2.0.14 I improved the error messages
a little. Is this from 2.0.14 or earlier?

> but -- is there any way to limit the number of
> simultanous deliveries on either the dovecot director or the backend
> lmtp-servers ? 
> 
> Will "process_limit=10" work for "service lmtp"? 

It'll work for both directory and backend, yes. Although each lmtp
process can also handle multiple clients. So you might also want to set
client_limit=1. Actually that could be a good idea to try in any case to
see if it helps with these problems.