I'm appealing to the wise to confirm what I am guessing to be true. I have a firewall with 2 active WAN interfaces, call them WAN1 and WAN2. MX records point from outside to WAN1. The first time I plugged in WAN2, I was blackslisted in about 20 minutes since mail was flowing out both WAN interfaces. Return route checking only verified on WAN1, so I was a "spammer" on WAN2. I don't want THAT to happen again.
So, do I static route my local mail IP to WAN1? Seems obvious, but I'd rather ask before borking my mail system again.
Firewall stats: Watchguard Firebox X750 Core w/WSM 11.4
WAN1: T1 (expensive, reliable, tiny bandwidth)...primary (lowest order) WAN interface
WAN2: DSL (cheap, unreliable, bigger bandwidth)