I’ve seen questions on the use of the /3GB switch recently in several different places, so I thought it useful to write up a very quick guide on where it should or shouldn’t be used. There are 3 basic rules for Exchange 2003:
* Implement the /3GB switch on mailbox or public folder servers that have 1GB RAM or more.
* If Exchange 2003 is running on Windows 2003, implement the /USERVA=3030 switch as well.
* Do not implement the /3GB switch on front-end or routing servers, even if they have 1GB RAM or more.
Ripped From: [MS Exchange Blog]