Routing email in multiple servers environnement.
For multiple reasons, in case of the web server and the mail server is not the same host, it would be mail server (and only mail server) to have to send email.
eg. If you have SPF and DKIM records in your DNS zone, web server will be "treated" by mail server as unknown/spam, and external server (other ISP) know her as a spammer.
The correct/logical topology is:
- Web servers relay all mail traffic to mail server
- Mail server(s) authorize traffic from web servers
We need to add in mail server's (this part is pretty easy) /etc/postfix/main.cf: mynetworks = [..], webserver(s) ip
and in web server's (it's hardest part to "manage")
The problem is Sendmail must relay to the right server (if the environment have multiple (not mirror) mail servers).
I'm not well documented with Sendmail (I'll fix that) to find a manageable solution from ISPConfig (automatically if possible). If someone have suggestions, i'm open to anything. I consider this like an important problem from ISPConfig, because the other services cohabit fine in a multiple servers environment.