Exchange 2007: PrepareAD could interfere with Exchange 2003 mailflow

A reported mailflow problems shortly after running Exchange 2007's /prepareAD, or after they installed their first Exchange 2007 role (which auto-launches the pre-requisite prepareAD process).  Through determining root cause, we found that this problem might affect a larger set of our customers that have (or have ever attempted) e-mail domain name sharing and use the "forward […]

A reported mailflow problems shortly after running Exchange 2007's /prepareAD, or after they installed their first Exchange 2007 role (which auto-launches the pre-requisite prepareAD process).  Through determining root cause, we found that this problem might affect a larger set of our customers that have (or have ever attempted) e-mail domain name sharing and use the "forward all mail with unresolved recipients to host" option.

What happens? Some of the Exchange 2000/2003 mailflow problem symptoms include:

- Messages eventually accumulate in deferred delivery queues - mostly on bridgeheads.

- In some cases, message tracking shows some messages routing back and forth a small number of times between the same Bridgeheads and mailbox servers.

Why does this happen? The e-mail domain name that users primarily use was ambiguously nonauthoritative. /PrepareAD does not expect this condition when enumerating recipient policies, and attempts to "fix" the Exchange 2000/2003 mis-configuration by making e-mail domain(s) consistently non-authoritative on recipient policies. A few other things occur behind the scenes, but eventually mail will queue-up.  If you only have a handful of recipient policies, here's how to determine whether or not you are at risk of a mailflow outage[…]

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