Exchange: Internal Email

It is possible for email to be delivered internally (within your Exchange Organization) without any need for MX records.  The reason being that your own Exchange servers can resolve the delivery request with a plain A (Host) DNS record.

For example, suppose you have two Exchange 2010 servers, Worcester and Boston.  Active Directory will already have DNS A (Host) records for these servers. So when mail is sent by a user with a Worcester mailbox to eddie @cperf.com, Exchange queries Active Directory for eddie's mailbox - answer Boston, then it queries DNS for the IP address of Boston. Now it can deliver email to the Boston Exchange 2010 server. No MX records are required for this scenario.

Summary of Exchange MX Records

1. There are three separate DNS challenges for your Exchange 2010 server.
2. If you are receiving email from the internet, then it is essential to configure MX records for your Exchange 2010 server.
3. Internal email delivery on needs A (Host) DNS records.
4. See more about Exchange MX records