Postfix MailRelay Setup confusion
I've inhereted a setup for 2 Postfix servers and an Exchange server.
I'll explain the setup first and maybe some of you Postfix Gurus can help me out here.
We have an Exchange server at the moment which is named: email.mydomain.com
It is not externally accessible.
We then have a Postfix relay named: mail1 and mail2 (same server, two different interfaces on two different T1 providers... this is just in case either of those connections goes down).
Currently our MX records are setup to have mail sent to first mail1 and if the fails mail2.
So that catches the event that if one of our internet T1's go down.
We then have a colocation server offsite (which at the moment isn't active), but it's named mail3. This offsite server is setup to connect to our internal network using OpenVPN. So it gets an OpenVPN internal IP.
What we would like to setup for is a failover server so that in the event of a full site outage (power-wise). Meaning mail1, mail2 AND email (exchange server) is down, mail3 will be our catch all relay, and store up the incoming mail until our Exchange server comes back up.
I'm trying to wrap my head around the best possible setup for this, so please let me know any guides or configuration options I should be aware of to make this happen.