MX records priorities & redirection

Question

I've noticed the mail records such as below and somehow the mails I receive from the domain come from the one with the higher priority (bottom one). I think it should have been using the other one.

test.com.   37536   IN  MX  10 test123.com
test.com.   37536   IN  MX  30 something.com

How is that possible? Do you think this is a redirection issue? It sends it the top one and it redirects all the mails to the bottom one? And for outbound emails, it probably does not even matter as it looks at the destination mx record. Am I correct?

Answer 1

Its possible a number of ways, and is unlikely to be a redirection issue.

The way things are "supposed" to work is that a mail server will try the MX 10 record first, then if its unavailable try the MX 30 record. Of-course, this is just a program doing what its told to do.

Some cases where this will occur -

• Some spam software deliberately tries the higher MX record in the hope that it will be less well protected then the main server.

• The primary mail server uses grey listing - which says "sorry, try later" whenever a sender/receiver/ip set is new to it. In this case, a sending mail server will probably simply try the backup MX.

• The main server had reachability issues from somewhere on the Internet so the sender fell back to the backup MX.

You are correct that it does not matter for outbound emails (in most cases)