Here is a good website to test and make sure your DNS records are set correctly:
A good way to test an email server on windows is to install telnet then connect to the mail server you want to test
telnet fabozzi.net 25
then type
ehlo fabozzi.net
and you should get a response press Ctrl+c then type quit to exit
On Linux runt he following command:
curl fabozzi.net:25
This will then return a response for the server if connection is successful
