Hi Example topology: Outlook 2007 SP2 > Exchange 2007 SP2 Mailbox Server > Exchange 2007 SP2 Hub Transport > TrendMicro SMTP Gateway > INTERNET Scenario: User1@domain.com sends an email to user2@domain2.com I have been scouring the internet in search for some answers, but hope someone can help me on the following: 1. As I understand it, from a client perspective, the email goes to their Outbox, where it is picked up by the Mail Submission service running on the Hub Transort and a copy is sent to the Hub Transport. Once that is completed, the message is moved to the Sent Items folder? Am I correct? 2. If the message is still in the Outbox, then this means the HT has not picked it up 3. We have 15MB message size limit set on our Hub Servers. Am I correct in thinking that if a user sent a 15MB attachment, this would still flow through the Exchange Mailbox server and only be rejected when it hit the Hub Transport?

1. The mbx server (sub svc) notifies the HUB that there's mail in the outbox for a mailbox, it retrives this and processes the message. 2. In theory yes, you could have a situation where there's a message stuck in the outbox and it constantly being submitted and picked up by the sub svc then to the hub, but generally your thinking is correct. 3. No , it wouldnt get sent throguh, it will just be rejected otherwise it would be a waste of resources sending the 15MB message and then being rejected once it hit the HUB. 4. However, it does depend how you have set your message limits, see below under section Order of Precedence for Message Size Limits , if set correctly then the message wont go through to the next hop in the transport pipeline. http://technet.microsoft.com/en-us/library/bb124345(EXCHG.80).aspxSukh

1. Here is the architecture: http://technet.microsoft.com/en-us/library/aa996349.aspx 2. You would think, but not necessarily so. Outlook/Exchange 2010 ( and even Outlook/Exchange 2007 combo) has issues with messages that arent in the outbox in cache mode, but appear in the outbox in online mode. The messages have actually been sent, but the sync process somehow failed. You'll find many who have experienced this - including myself.( http://social.technet.microsoft.com/Forums/en/exchange2010/thread/c6277c33-3f5a-47b2-9712-6cc570b4d6ba) So my answer to that is, it depends. If you are in cache mode, and the item doesnt leave the outbox, then most likely it wasnt sent for whatever reason. Another thing to note, the Outbox is not visible in OWA 2010 Premium. 3. That depends on the client. Lucky for you, you are using Outlook 2007. In that case, it should never let you actually send the message ( Nor will OWA).

Hello All Regarding #3...an Outlook 2003 client will send a 15MB message onto Exchange mailbox server, but an Outlook 2007 client won't? The reason I thought the message would be sent is because the message size limits are applied at the Hub Transport layer, not the Mailbox layer, so I figured the Mailbox server would still accept the message?

Early versions of Outlook 2003 would actually attempt to send the message, then Exchange would reject. After Sp1 or maybe SP2 of Office 2003, the message would not be sent at all. Remember, when you are in mapi mode, Outlook is closely integrated with Exchange, so it can check the Org message limits w/o actually sending the message.