Firstly - your
MX record MUST point to hostname that itself points to an
AAAA record. An
MX record cannot directly contain an IP address nor can it point to a
Secondly, ideally it should point to whatever your
HELO name of the server is, but if they're not going to match nomatter what, then it doesn't matter where it points to, just as long as the
A record resolves to the correct IP address.
You can verify your MX is set up correctly by using nslookup (windows) or dig (linux). On nslookup you would do this:
Default Server: dns.domain.local
> set q=mx
example.com MX preference = 10, mail exchanger = mail.example.com
mail.example.com internet address = aaa.bbb.ccc.ddd
If you see your correct IP address on that last line, then your MX is working correctly.