Before you say anything...I know that Microsoft documentation states that E2k3 FEandE2k7 MBX is not a supported configuration.Here is my situation...We aretransitioning to Exchange 2007 from Exchange 2003.User mailboxesare on E2k3 BE servers. I deployed all E2k7 server roles including CAS. We have not yet made the change however, to force users to use the CAS server, they still use the E2k3 FE. I moved my mailbox onlyto the E2k7 MBX server. Currently,only my mailbox is using E2k7 MBX and an E2k3 FE. OWA is broken but ActiveSync still works.My question is, does this configuration have some adverse affects such as corrupting mailbox data or is it simply not supported? If it will have some negative affects, I will turn off my ActiveSync. If it works but is simply unsupported, I will leave it on until we are "Internet-ready" with the CAS servers.Thanks,Micah

It will not "damage" anything but OWA 2003 is not aware of OWA 2007 and therefore cannot proxy properly. If you move your mailboxes before you move toOWA 2007 users will be able to connect to Exchange 2007 using MAPI without issue. Only "front-end" features will be affected.Also understand that if you switch to OWA 2007 today, it will properly redirect users back to 2003. So I would move to OWA 2007 today, then as you move mailboxes the OWA 2007 will do less and less redirecting.Read up on this before you move. Also understand how redirection "breaks" when you dont give it a dedicated server. http://msexchangeteam.com/archive/2007/10/12/447266.aspx http://msexchangeteam.com/archive/2007/09/10/446957.aspx http://msexchangeteam.com/archive/2007/09/04/446918.aspxMike Crowley: MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator