There are two problems shown in the output you've provided. The first on is (this is usually the cause of the problem) there is no MX record shown in the output you've provided. The second problem is that you're not actually using the correct command to display the output of the DNS records. The commands you're using "dig cs2.fstrf.org mx" is wrong (you're using the FQDN of the server not the domain name), it should be as follows (unless you're using a sub-domain for a specific reason?):
If I use the correct domain name for the dig commands I get a different IP address than the one in your dig output. You either have a problem with your DNS configuration or you're using the the wrong command.
As this isn't a new install or an upgrade I guess I can assume it's been running for some time? If that's the case what precipitated this problem?