nginx as pop3/imap proxy

[Maxim Dounin]

Hello!

On Fri, Nov 07, 2014 at 03:34:48PM +0100, Andrea wrote:

> Hello,
> I'm using with satisfaction nginx as pop3 and imap proxy of 4/5 mailservers.
> 
> I have just one problem:
> when one server is down, nginx can't authenticate the user and the user
> mail client request the password as if it's wrong.
> Without nginx, if one server is down, the user just can't connect to it,
> but there's not an authentication problem.
> 
> So, my question is:
> is it possible to configure nginx to manage in some different way this kind
> of situation? Best, but maybe not implementable, would be nginx to simulate
> a fake connection even if the server is down, so when it comes up again the
> user just see a delay with the received mails.

As of now nginx tries to be as clear as possible that the problem 
is not with an authentication.  In particular, for IMAP it uses 
the BAD response rather than NO:

http://tools.ietf.org/html/rfc3501#section-7.1.3

I don't think that such a distinction is possible with POP3 
though, and also has no idea if mail clients are smart enough to 
understand the difference in case of IMAP.

The idea to simulate a fake connection looks very wrong for me, 
but something like closing a connection without returning anything 
may work well.  But I think we need more information about client 
behaviour to find out what can/should be done here.

-- 
Maxim Dounin
http://nginx.org/