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CentOS 5.x | SendMail

This is somewhat related to my other question about round robin but as it's more general, I thought I'd separate it out.

If SendMail is smarthosting to a FQDN with multiple A records and it can't reach the first host it tries, will it immediately retry connecting to one of the others? Or will it defer the message and try again during the standard queue runner interval?

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up vote 2 down vote accepted

The bat book says:

As usual, trying a host means trying its MX records first, or its A or AAAA record if there are no MX records


When sendmail finds multiple A or AAAA records for a host (and no MX records), it tries them in the order returned by DNS, but looks up and uses AAAA before A records. If sortlist is specified in the /etc/resolv.conf file, DNS returns the A or AAAA record that is on the same network first. The sendmail program assumes that DNS returns addresses in a useful order. If the address that sendmail always tries first is not the most appropriate, look for problems with DNS, not with sendmail.

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Thanks for the prompt response but I'm still confused. What if there are multiple A records and the first one is unavailable? – Mike B Aug 22 '12 at 17:25
I updated the answer. – adamo Aug 22 '12 at 17:33
Perfect. Thank you! – Mike B Aug 22 '12 at 20:30

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