I've been looking at various docs regarding how to create a backup mail server using Sendmail under Linux.
One set of docs seems to suggest that all I need to do is to add the domain for what I want to act as a secondary mail server for to /etc/mail/relay-domains and set the MX records so that the primary mail server has a higher priority (lower number) MX record than the secondary mail server.
Eg:
adomain.com. 86400 IN MX 10 mail1.adomain.com.
adomain.com. 86400 IN MX 20 mail2.adomain.com.
I tried that, and it works while mail1 is up, but when it's down I get:
553 5.3.5 mail2.adomain.com. config error: mail loops back to me (MX problem?)
554 5.3.5 Local configuration error
Other docs suggest adding mail1.adomain.com as a delivery agent
or adding an alias
*@adomain.com %1@adomain.com
1) Why doesn't simply adding the domain to /etc/mail/relay-domains work (assuming the appropriate MX records are in place)?
2) What's the "right" approach? Adding mail1.adomain.com as a delivery agent feels wrong as does adding the alias. Why should that help??? [Or do they mean
*@adomain.com %1@mail1.adomain.com
I could see why that would work, but it feels like a cludge]
I've also looked for useful sendmail docs relating to this, but with little success. Pointers please?
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