Closing Out Exchange Mailboxes

9. Deal with Legacy Delivery
When you finally remove the mailbox from the Exchange server (or sooner, if you remove the primary SMTP address), you might find that message transport resources incur increased traffic. That traffic increase occurs because the system has to generate and deliver an NDR email message in response to every message someone sends to the legacy SMTP address. If you're running Exchange Server 2003, configuring recipient filtering is a simple and easy way to block messages sent to legacy addresses over the Internet.

Using the MMC Exchange System Manager (ESM) snap-in, open Global Settings, Message Delivery. On the Recipient Filtering tab, select Filter recipients who are not in the directory. For each SMTP virtual server that you want to accept inbound SMTP mail, click Advanced on the General tab, click Edit to display the IP Identification options, then select Recipient Filtering. Click OK, then stop and restart the SMTP virtual server. The next time someone sends an email message to the legacy address, the SMTP virtual server will query AD to check the address. When it finds the address, the recipient is accepted; if it doesn't find the address, the recipient is rejected. . . .