I have just installed SBS 2008 for a client. However I have a problem that when I send an email to that exchange server from an email client (outtlook etc) I get
The mail server responded: 5.1.1 <email@example.com>... User unknown. Please check the message recipient firstname.lastname@example.org and try again.
However if I send an email to the exchange server using gmail it gets sent and is received by the user. Starting to pull my hair out over this