AuthRequired for Exchange 2007 distribution groups

When creating distribution groups in Exchange 2007 'Require that all senders are authenticated' is on by default (under Properties/Mail Flow Settings/Message Delivery Restrictions) leading to 550 5.7.1 RESOLVER.RST.AuthRequired errors.

More at TechNet.

Using NSlookup.exe

Useful for checking DNS settings, the most basic command is:

nslookup [hostname] [server]

More at Microsoft's support page. Linux uses host with more advanced alternatives being dig or drill.