Exchange 2007 UM sizing

Had an interesting exchange with Microsoft’s Michael Khalili in which I finally learned how many angels can dance on the head of a pin. No, actually, I learned what Microsoft’s recommendations are for Exchange 2007 UM server sizing. Michael’s guidance is that a single dedicated UM server can handle up to about 100 concurrent telephone calls (the nunber obviously varies according to your hardware configuration and which gateway you’re using). If you have fewer calls arriving concurrently than that, you can happily colocate the UM role with other server roles.

Note that this has nothing to do with the number of users, mailboxes, or PBXs– it’s just a guideline for the number of ringing phones you have to support at once.