Sendmail and backup MX

[Kevin Miller]

Steve Campbell wrote:
> I believe DNS does this if you have your secondary MX defined in DNS
> with equal or lower priority than the primary.
> 
> The primary will not accept mail as it's down.
> DNS will direct mail to the secondary automatically.
> 
> I think this is all proper. I could be wrong though.

Yes, that's right more or less.  Except that in practice the primary doesn't
have to be down - if it's up but momentarily busy the sender may fail over
to the secondary.  Also, many spammers target the lower priority servers, on
the assumption that they're less likely to be updated w/the latest greatest
spam filters.  I have a terciery server that sees maybe a dozen real mails a
day, and several hundred high scoring spams.  I'm quite content to let it
vaporize spam and send nary a real message - takes the load off my other
mail servers.

Don't have any examples for the OP, but I'd venture that a script in cron
that checks for port 25 on the primary should be pretty easy.  If it fails,
have it kick off sendmail on the 2ndary.  There's a number of status
checkers out there...

...Kevin
-- 
Kevin Miller                Registered Linux User No: 307357
CBJ MIS Dept.               Network Systems Admin., Mail Admin.
155 South Seward Street     ph: (907) 586-0242
Juneau, Alaska 99801        fax: (907 586-4500

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