Re: [courier-users] Strange Feature Request...hints/ideas requested

[Jeff Potter]

If PHB's just want something 'redundant', do:

1. set up 2 boxes w/ courier; box A and box B.
2. set MX records for mail.domain.com pointing to both A and B; give A priority 10, B priority 20.
3. set all mail to be delivered to, say, /home/mail/X (on both boxes; although when everything's up, all RFC-compliant servers will use server A to send incoming email)
4. rsync A->B every hour, 30 mins, whatever.
5. set DNS for pop.domain.com pointing to A. Run a health-check script on your DNS server that modifies the value of pop.domain.com to be 'B' when 'A' is not accessible. When 'A' becomes available again, run rsync B->A. If you want to be really fun, run DNS on physical box A and B, have domain.com delegate mail.domain.com and pop.domain.com to your 2 boxes; have A always return only its own values, have B return A's values but modified when A is inaccessible. Since DNS queries time out after ~2 seconds and try the next known name server, you can effectively get a poor-man's failover this way.

You will probably lose some email on the boundry cases unless you are very careful about syncing the two boxes and having the DNS correctly switching. (You should also probably not run the mail server on the box that's not the 'live' one at any give time -- spammers seem to love secondary mail servers.)

I wouldn't recommend doing this -- you're bound to cause more pain than you realize. Maybe there's a better way??

cheers,
Jeff



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