We are currently running a single Exchange 2007 SP1 with RU3 (CAS, HT, MB).I'm about to introduce a 2nd Exchange server into our other Data Centre (CAS, HT, MB).1/2 our mailboxes will be migrated to the new server.The original server will be a CAS proxy for the 2nd server.I'm unsure if I should:Install to the same version level as our current Exchange serverORInstall as SP2 with RU2Are there any issues with running 2 Exchnage servers in different sites on different version.I will be planning to upgared the original server to the latest version after a cool off period.Regards,Steve

Hi,It could be. Use SP1 as proxy for SP2.But as SP2 release notes said: recommend that you upgrade Client Access servers that reside in Internet-facing sites before you upgrade Client Access servers that reside in sites without Internet connectivity.http://www.microsoft.com/downloads/details.aspx?FamilyID=ee7829a3-0ae8-44de-822c-908cd1034523&displaylang=enFrank Wang

Hi Frank,Thanks for pointing that out for me!

For Your Information:You can not CAS-CAS proxy from Exchange 2007 SP1 > Exchange 2007 SP2.I have unfortunately found this out the hard way and will upgarding our other exchange server this weekend.

Hi Steve,Thanks for your information. Could you please provide more details where you find the solution? A link about it is better.Thanks.Frank Wang

Sorry don't have a link.I found this out by doing it.I had our original exchnage 2007 server (HT, CAS, MB) on SP1 RU3.I installed a 2nd exchange server in a different AD site (HT, CAS, MB) on SP2 RU2.The SP1 server was unbale to CAS proxy for the new server.If you try this in OWA you actaully get an error message stating that the SP1 server can not proxy for the SP2 server.I upgarded the server last night so they are both running SP2 RU2.CAS-CAS proxying now works as expected.

Hi Steve,Thanks for share. :)Frank Wang