Mailbox deleted or simply overwritten?

I'm pretty sure it's full-on delete. Remember too that there are thresholds available to control the behavior - i.e. don't delete a mailbox if it's bigger than x. This concept was introduced to deal with the auto-instantiation of mailboxes that began to plague migrations around Exchange 2010.

Does it store any data about the mailbox before deleting, and then reapply it to the new? Kind of like it does when it matches a source mailbox to a target contact. In our test the legacyExchangeDN did not change.

Here is a KB that discusses that parameter in more detail.

support.quest.com/.../72579

Remember that the DSA creates a stub mailbox for the most part. Then it's Exchange that physically creates the mailbox. The MTA creates the mailbox that was created and it leaves the attributes alone.

Correct, but in this case the mailbox exists in the target first. Then I let the DSA run, then calendar sync. So it deletes the existing mailbox for the same reasons stated in that article, and re-creates it. But it appears to be saving those attributes and applying them to the new mailbox. Customer is just looking for confirmation on that as I also thought it was a full-on delete.

The attributes are the same because the AD Account is not deleted, just the mailbox that Exchange deletes. The Account is still intact.

Thanks!