How to Email Enable an Exchange 2007 or 2010 Distribution Group to work from the Internet (or how to fix 5.7.1 smtp;550 5.7.1 RESOLVER.RST.AuthRequired; authentication required)

If you get this… 5.7.1 smtp;550 5.7.1 RESOLVER.RST.AuthRequired; authentication required

It is likely because you haven’t allowed an Exchange (2007 or 2010) Distribution Group to receive email from recipients outside of the Organization (Exchange Organization/Active Directory). The default is Distribution Groups DO NOT ACCEPT Internet emails.

Here’s how the email NDR will look…

Here’s the solution