Hi, After installing Exchange 2010 into our organisation, we intermittently have one or two users who can no longer connect Outlook 2007 to their 2007 mailbox. OWA access is okay. A work around is to move them to 2010 but that project has been put on hold (Outlook Add-in compatibilty issues). Rebuilding their profile does not work. A packet trace shows "unknown?! request" and "Unknown?! response" MAPI errors. I've seen some posts regarding Broadcom nic drivers but we are using HP kit. Anybody seen similar issues?

Hi, To narrow the root cause, I recommend you first try to connect the user's mailbox by using another computer. If you can connect to the mailbox without problem, the problem should reside in the user’s computer. If the issue persists, please try the following steps: 1. On exchange server 2007, create a new mailbox database. 2. Move the user's mailbox to this new mailbox database. Then test to see if the issue persists.Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Thanks Gen Lin-MSFT