feature request: smtp auth passthrough

[Michael Both]

Hello,

sorry for that beforehand, but yes, I'm another newbie using (or at 
least trying to use) NGINX in a mail proxy setup.
I read the wiki entries and docs beforehand... and I thought it just 
works like that (passing auth to backend).
So actually I was rather shocked that authentication is not passed to 
backend SMTP servers opposed to POP and IMAP backends.
As for our deployment, it would be a pain in the arse to import login 
data from our backend servers.

So research a bit and at least I'm not the only one trying to use a 
setup like this.

http://mailman.nginx.org/pipermail/nginx/2008-April/004234.html
https://www.ruby-forum.com/topic/1045106
http://mailman.nginx.org/pipermail/nginx/2010-February/019028.html
http://mailman.nginx.org/pipermail/nginx/2010-April/020027.html
http://mailman.nginx.org/pipermail/nginx/2010-November/023555.html
http://mailman.nginx.org/pipermail/nginx-devel/2012-April/002074.html

David Jonas even wrote a patch addressing this issue.
But as we only use official distribution packets, and also his patch is 
for a quite old nginx version, that won't work for us.

Hence I kindly ask of you, also in the name of my predecessors and 
everyone else looking for a solution like this, to implement a method 
for passing smtp login information to the backend server in one of the 
next versions.

Best regards and a happy new year!

Michael Both