Exchange 2007 and Exchange 2003 and the eternal mail loop

We recently added x07 to our domain, doing the standard migrate from x03 over to a new box. Everything went surprisingly smoothly except for a few 'glitches' of which I will write more in different blogs.

What I want to talk about today is an issue that arose due to the requirement that our outgoing email continue to be sent through our x03 system and not our brand, spanking new x07. I won't go into the reasons involved, but suffice to say we had our marching orders.

One of the beauties of all the work MSoft has poured into x07 is how remarkably it plays well with others, or at least with x03. We moved the mailboxes and it did not matter whether incoming mail hit the x03 or the x07, it got delivered correctly. The reason for this is that x07 automatically a routing connector to the old x03 system that routes it to the x07 system (if boxes are not local). This is wonderful, but it also tripped me up.

I had assumed that the solution would simply be to add a Send Connector to the X07 box. Basically anything that was going to be routed via SMTP would be directed to the old x03 box. It was very simply to setup - go into the Exchange 2007 Management Console, go under Organization Configuration and thence into Hub Transport. Select the Send Connectors tab, right-click and select "New Send Connector...".

I won't go into how to create a new SMTP Send Connector, it is fairly straightforward -> give it a good name; specify that this is an "Internal" connector (we are all on the same team after all); add the address space of * and an appropriate cost (I initially selected 20 but just make sure it is lower than what you have for the rule sending to your Edge server); select to route through a smart host and specify the X03 box as your smart host; I chose "None" for my authentication since this was for testing; and voila!

It initially appeared to work and then all of a sudden emails were getting hung up. Sending an email threw it into a void until eventually an NDR would be generated with the following line:

Oops.

The culprit, of course, is that each of the two systems, x03 and x07 have routers that send the email back and forth. They are so happy doing such a thing that they won't pass it out, just back and forth, back and forth, back and forth.

My initial thought was to see if I could modify the Routing Connector that was automatically added by x07 during the install. It had a weight of "1", which meant that it was THE rule. As a result, the rule that goes to the Internet is ignored (having been bumped up) and evertime the x07 system passes an outside email to the x03 system, the x03 system insists on passing it back. However, I know of now simple way to do this. Opening up the router in x03's System Manager results in the following error "Exchange System Manager version 8.0.30535.0 or greater is required to edit this object. See About dialog for version information". So that won't work. The Send Connectors section of the x07 Management Console does not show this. I am sure there is an easy way to do this (probably through powershell) but I did not find one.

So instead, went back to the x03 box and set the internet smtp route to ALSO have a value of "1". For some reason which I can not easily fathom, mail started to flow through the x03 box. What confuses me is how the x03 box, having TWO connectors of value "1" seems to select the correct one. Perhaps it automatically selects the earlier one, or perhaps it is something as odd as the fact that the x03->Internet connector comes alphabetically before the x03->x07 connector.

What ever the solution - I would like to close with that old, old MSoft test answer which sadly disappeared a while ago - "Solution should not works, but appears to".