I have some distribution lists, size doesn't seem to matter. None are dynamic. When someone sends to a distribution list, the mail item makes it to the "MapiDelivery" queue, and there it sits. Once it goes Active, it holds up all the other mail in the queue. It will stay active for as much as 2-3 hours. Once the DL mail item has finished and clears out, the rest of the mail items in the queue will empty rather quickly. While this is going on, "store.exe" and "EdgeTransport.exe" will hold CPU utilization at 100% -- when done, CPU utilization will return to about 10%. Drive I\O is negligible, so I don't think it's storage related.There was no issue with this a few days back, it started suddenly without any clue as to why. At the time, I was running SP1 with UR 7. I puton UR 9, but nothing changed. Went ahead and put on SP2, but still no change. I've looked everywhere I can think to look. The event log is clean, I don't see any errors elsewhere. I've removed antivirus, tried turning off transport agents, anit-spam, etc, none of it did any good.I'm at a loss -- any ideas what I should check next?

humm.... I have not seen this. We have been on SP2 now for about 2 weeks on my main E2K7 system. And our users LOVE DL's. Does your DLs specify an expansion server? Is your connectivity to a local GC good? Jim McBee - Blog - http://mostlyexchange.blogspot.com

Me neither. Removed anti-virus? What kind? ANy other 3rd party software installed? ExBpa show anything?Absolutely nothing in the event logs when this is happening?

Not specifying an expansion server, but at the point where they're getting stuck, they already appear to have been expanded -- though I'm not sure exactly at what step that occurs.Did have Forefront installed, but removed it thinking that may have been the cause. There are no other applications installed -- just Windows and Exchange. Ran ExBpa and the only thing that came back with was a change to DatabaseMaxCacheSize in EdgeTransport.exe.config -- restarted the server afterwards just to be safe, but still nothing.The only thing that has started to come up in the event log is this, but from what I understand, it just means the person has hit their mailbox quota:Event Type:ErrorEvent Source:MSExchangeIS Mailbox StoreEvent Category:Logons Event ID:1022Date:9/21/2009Time:10:31:20 PMUser:N/AComputer:MAIL-SRV1Description:Logon Failure on database "First Storage Group\Mailbox Database" - Windows account NT AUTHORITY\NETWORK SERVICE; mailbox /o=[removed]/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=[removed].Error: 1245 Client Machine: MAIL-SRV1 Client Process: edgetransport.exe Client ProcessId: 0 Client ApplicationId: Client=Hub TransportI keep hoping to find that magic checkbox somewhere that will make me feel stupid for not finding it in the first place. Until then, I keep digging.

Distribution List (DL) expansion takes place on the Hub in a round robin fashion (By default). Does Require that all senders are authenticated have been checked in the Properties of mailboxes of the recipients? Will the issue happen to new created DL?

I would run DCDIAG and netdiag to DC and GC's when this issue happens and see, if for any reason Exchange is loosing connectivity with them. I would also create one Test DL and check to make sure if the issue relies with specific DL or all DL'sVinod |CCNA|MCSE 2003 +Messaging|MCTS|ITIL V3|