Unable to send and receive mails from some domains
I'm quite new to Zimbra and mail servers as a whole. We have set up zimbra mail server and we are able to send and receive email from and to almost everyone. The "almost" part is what we don't like currently. There is a domain that we cannot send emails to. It seems that their revers DNS is not configured properly. In the same time they have 2 MX records with different priorities (set correctly). However the one with the lower priority is the one that responds to our efforts to send emails.... which is odd.
Any ideas? Can we force Zimbra to send emails to a certain MX record?