While I run a backup job (backup exec 11d, win2003, GRT only) for my exchange 2003 server, my BES (which always work fine) works very slowly and email are delivered to devices after a long time if ever). Once the backup is done (or being stopped) then everything returns to normal.
One strange thing is that ActiceSync and Outlook clients are not affected by the backup job. My store is 160GB.
I have a dell tape library that works pretty fast for files.
I contacted RIM's support and they say that the BES threads are failing to communicate with the server. This happened also with an older version of BES.
I don't see any high memory or CPU on the exchange server.
Thanks much for your help!