Hello!

On Sun, Apr 05, 2009 at 01:30:34AM +0400, Anton Yuzhaninov wrote:

> Atif Ghaffar wrote:
>> If I correctly undrestood,
>>
>> 1. nginx as smtp proxy is useful when using smtp auth. (to dispatch to
>> different backends)
>
> IMHO nginx as smtp proxy with auth useful only to reuse auth server created for pop/imap proxy.
>
> For pop3/imap nginx need for proxing different users to different backend (where mail stored).
> In smtp message can be send via random server.
>
> nginx can be used for load balancing between different servers with MTA,
> but for load-balancing only better to use something like IPVS (in Linux)
> or pf (in BSD).

No, you are somewhat wrong here. As smtp proxy with auth nginx is
really very usefull to move load away from traditional
process-per-connection smtp servers (until user is authenticated).
This saves lots of resources when you have many invalid
connections (e.g. initiated by malware, bruteforce attacks etc.).

This may not be an issue unless you run big mail server
though.

>> 2. nginx as smtp proxy is useful when not using smtp auth. (to do ip
>> based checks)
>
> Without auth (incoming mail) nginx can be used to save resources if only
> ip not in RBL proxied to servers with MTA.
>
> But I don't know is current nginx version used anywhere in production as
> smtp proxy without auth. IMHO it not ready for production, because of
> lack smtp pipelining support. Some MTA (probably some sendmail
> versions/configs) have bad habit to use pipelining even if it support
> not adversed in EHLO reply.

Yes.

Support for smtp pipelining may be found here:
http://mdounin.ru/hg/nginx-mail

Maxim Dounin