Due to a typing error (on my part) you've not given me the correct output for one of the dig commands, it should have been the following:
There also appears to be no A record for your mail server in the output you've posted.
dig tribley.org any
While it's not incorrect to have a priority of zero on your MX records it's usual to have higher numbers than that. You've also got two records with the same priority, do you really have two mail servers in this domain?
Your hosts file should really contain only the following (unless there's some reason you have two hostnames for this server?):
Could you confirm if you have disabled the firewall and SElinux on this server?
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 localhost.localdomain localhost
192.168.1.188 mail2.tribley.org mail2