very few of my users have intermittent problems sending e-mails and it is staying in their outbox - what is the best way to find out why the mail is not being sent out? our setup is as follows:- latest rollup of exchange 2007 Version 8.1 (Build 240.6) running on windows 2008- CCR and SCR on the mailbox server- cas and hub running under hyper-v- 294 mailboxes in two databases on separate RAID10s(SAS); each database is ~35Gb- 16Gb RAM for mailbox cluster nodes; 2xCPUs Quadcore Xeon 3Ghz

Hi, Firstly, I would like to explain the process the message is submitted to hub transport server. When the Mail Submission Service on mailbox server detects a new message is available, it picks an available Hub Transport server in the same AD site and submits a New Message Notification to the Store driver on the hub transport server. Once a Hub Transport server has been notified, the Store driver will connect to the users Outbox folder and collect any messages that need to be sent. The Store driver then submits those messages to the Submission Queue and moves the message from the users Outbox to their Sent Items folder. Therefore, I suggest you firstly increate diagnostic level of store driver and mail submission by using following command: On Mailbox Server: Set-eventloglevel msexchangemailsubmission\genernal level expert On Hub Server: Set-eventloglevel msexchange store driver\generanl level expert Then, reproduce the issue and check whether any event is logged regarding the issue on mailbox and hub server. In addition, please also check event log on hub server and ensure no back pressure related event. For more information regarding the back pressure, I suggest you refer to following article: http://technet.microsoft.com/en-us/library/bb201658.aspx If the above information does not provide any clues, you may need to use extra to capture a storedriver trace on mailbox server and hub server to gather further information in order to know what happened when submit the message in the Outbox folder. Mike