It’s inevitable that HR will terminate someone, IT will delete their AD account or mailbox, and only later find out that the department needed that person’s email to be forwarded to someone else. This isn’t a big deal for external senders. Just add the axed employee’s email address as an additional address on the new recipient’s mailbox. But what about internal senders? Anyone who has the axee in their Outlook autocomplete cache or who replies to one of their old emails will get an NDR (Non-Delivery Report).

The fix is simple. Add the former employee’s LegacyDN to the new recipient’s mailbox as an X500 email address. There are three ways to get the LegacyDN. Assume the former employee is named Joe Shmo.

1. Copy it from one of those NDRs. It will be in the details of the error message.
2. Get it from the disconnected mailbox in the Exchange Management Console, assuming that it hasn’t been more than a few weeks since the account was deleted. You’ll have to type it all out, though, so this isn’t ideal.
3. You can use this command to get that LegacyDN, which you can then copy and paste: Get-MailboxStatistics -Server [MAILBOXSRV] | ?{$_.DisconnectDate -ne $null -and $_.DisplayName -like “Joe Shmo”} | Select LegacyDN
   MAILBOXSRV = The mailbox server on which the disconnected mailbox resides.

Open the properties of the new recipient’s mailbox and go to the E-Mail Addresses tab. Click the drop-down button next to the Add button and select “Custom Address”. In the “E-mail address” field, paste the LegacyDN from above. In the “E-mail type” field, enter X500.

Now, anytime someone replies to one of Joe Shmo’s emails or sends a new email to the Contact they saved in Outlook four years ago, it should get to the right person instead of bouncing.