Supplemental to my "yours and mine gateways’ thread I’m looking at the alternative of a ‘static Equal-cost Multipath routing’ solution as per the manual, but foresee two problems - one of them a biggie.
I know it works because I’ve tried it for a (short) while, but each gateway is, for us, a separate ISP - and in this neck of the woods ISPs only accept SMTP traffic off their own networks. Thus there is a 50% chance that the mail app of a subscriber is going to try to send mail to the one defined in its SMTP server config via the ‘wrong’ network - which will probably be rejected. To a lesser extent the same thing happens with DNS servers - the is a 50% chance that the lookup addressed to the server defined in the subscriber’s box will go via another ISP’s network, with a few extra hops on the way.
Presumably rules can be added to catch these on route and direct them to specific gateways, but these will need altering every time either ISP changes an address for a SMTP or DNS server. Or is there an easy way?