Great news for Exchange Administrators!
I just saw this today posted on Gerod Serafin's blog. The Exchange team has posted a new KB article detailing a hot fix (yes, you still have to call in and get it, no you won't be charged for the call) that is now available to deal with disabled user accounts.

Prior to this hotfix, the default behavior was that as *soon* as you disable a user account, ALL mail will immediately begin to NDR. This is because disabled user accounts do not have a valid msExchMasterAccountSid attribute.

There used to be 2 methods to fix this (both arrived at the same solution, but one was automated). The first was to manually edit the ACL's on the account (Mailbox Rights) and grant the SELF account Full Mailbox Access and Associate External Account. This would fix the missing msExchMasterAccountSid attribute and allow the mailbox to again receive mail. The second method was to obtain a tool called NoMAS (No Master Account Sid) and run it. It would then automatically fix any and all accounts in the domain with this missing attribute.

I have always disagreed with this default behavior, so I am quite happy to see this hotfix available. It will change the behavior of Exchange so that it automatically uses the SELF sid as the msExchMasterAccountSid for disabled accounts. Read more about this hotfix from the following KB article.
KB 903158

Update: It has also been posted on the Exchange Team's blog, courtesy of Nino Bilic and Alex Seigler (Alex was the original developer of the NoMAS tool). Thanks go out to all those involved in publishing this hotfix.
- posted by Ben Winzenz @ 10:59 AM