Remember the song "I am my own grandpa"?

[Dan Brotsky]

Good! Because I'm currently puzzling over the best way to get SIMS to sing "I am my own backup," and I'd love some thoughts... :^)

Here's the situation:

1. I run SIMS on a firewalled internal machine, which appears to outside machines to be at "mail.brotsky.com" (which is actually the external address of my DSL modem/router/firewall).

2. When my DSL line goes down, my DSL modem knows to instead dial up my ISP, at which point its external address (and thus the visible address of my SIMS machine) becomes "backup.brotsky.com".

Here's the question:

Given that I control both the DNS info and SIMS config info pertaining to this situation, is there a configuration that allows me not to have to reconfigure anything when my DSL modem does its magic backup thing?

Here's the answer I've been working on so far:

1. mail.brotsky.com is MX priority 5, backup.brotsky.com (which never responds unless my DSL is down) is MX priority 10, my ISP backups are at priorities 20, 30, etc.

2. My SIMS primary "domain name" is mail.brotsky.com and backup.brotsky.com is aliased to it in the router (as is brotsky.com, obviously :^).

This answer works great for incoming mail, because machines that send to backup.brotsky.com couldn't care less that the machine that answers claims to be mail.brotsky.com. But this answer works much less well for outgoing mail, because servers that do reverse DNS confirmation more stringent than "make sure this IP is really listed in the MX records for the domain it claims to be in" do not like the fact that backup.brotsky.com is saying "helo mail.brotsky.com".

Anyone have a better idea? Especially one that doesn't involve changing either DNS entries or the SIMS config dynamically when the router switches over?

dan


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