Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.
One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.
2.) Set up all the users on the exchange server.
3.) Set the domainname you have in your mailertable file for sendmail.
4.) Send an ETRN from the Exchange server to the Linux box.
Your mail has now been switched, assuming you did the above correctly and are running a version of sendmail that supports ETRN.