I am in the co-existence phase. When the user with mailboxes on the Exchange 2010 system send email with multiple recipients that are on both Exchange 2003 and Exchange 2010 systems, the sender got a bounced message saying the message delivery is _delayed_. Upon looking further, I found out that the message did not reach the mailboxes still on 2003, however it reached those on 2010. (Messages to individual users from 2010 to 2003 seem to be ok.) Another migration question: do I need to convert all the global distribution groups to universal distribution groups? Thanks and regards.

(Messages to individual users from 2010 to 2003 seem to be ok.) Hi Fat Frog, If you send messages to multiple recipients on Exchange 2003 directly, does it work? Please use the "Tracking Log Explorer" on Exchange 2010 to track the delayed messages. "do I need to convert all the global distribution groups to universal distribution groups?" Yes, please convert the Global DGs to Universal ones. Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com. Frank Wang TechNet Community Support

(Messages to individual users from 2010 to 2003 seem to be ok.) Hi Fat Frog, If you send messages to multiple recipients on Exchange 2003 directly, does it work? Please use the "Tracking Log Explorer" on Exchange 2010 to track the delayed messages. "do I need to convert all the global distribution groups to universal distribution groups?" Yes, please convert the Global DGs to Universal ones. Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com. Frank Wang TechNet Community Support