We recently upgraded all of our DCs to Server 2008. Our mail server is Exchange 2003. If we start pushing our forest level up to 2008 will this cause any known issues with the exchange server? It is server 2003 SP2.

I don't think this will cause any issue with Exchange Server 2003 SP2. Exchange 2003 SP2 can work with forest level 2008. Exchange Server Supportability Matrix http://technet.microsoft.com/en-us/library/ff728623.aspx Thanks, Evan Evan Liu TechNet Community Support