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Mail forwarding without mailboxes

Exchange 2010 SP3 had 30 active users and 10 mailboxes belonging to former employees, for a total of 40 active mailboxes. The former employees' mailboxes had not been deleted because they forwarded mail to the users' personal addresses.

Task

Remove the former employees' mailboxes while preserving mail forwarding.

Solution

  1. Delete the mailbox and account.
  2. Create a Contact with the former employee's email address.
  3. Create a transport rule that forwards incoming mail addressed to that contact to the external SMTP address.

Rationale found later

When forwarding to an external MTA, this is the correct approach because it preserves the message in the proper form.

Initial setup: on host mail.forward-domain.com (Exchange), [email protected] is forwarded to [email protected]. mx.recipient-domain.com runs Exim.

Log when using a transport rule

2014-11-26 07:12:36 1XtUu2-0009VE-IR <= [email protected] H=mail.forward-domain.com [1.2.3.4] P=esmtp S=12223 1416978723[email protected] from ... for [email protected]
2014-11-26 07:12:37 1XtUu2-0009VE-IR => [email protected] R=my_relay_domains_router T=remote_smtp H=192.168.112.59 [192.168.112.59] C="250 2.6.0 <[email protected]> [InternalId=21955] Queued mail for delivery"
2014-11-26 07:12:37 1XtUu2-0009VE-IR Completed

Log when using the mailbox flow rule

2014-11-25 06:11:17 1Xt7T8-0001mj-RD <= [email protected] H=mail.forward-domain.com [1.2.3.4] P=esmtp S=18115 from ... for [email protected]
2014-11-25 06:11:17 1Xt7T8-0001mj-RD => [email protected] R=my_relay_domains_router T=remote_smtp H=192.168.112.59 [192.168.112.59] C="250 2.6.0  [InternalId=20870] Queued mail for delivery"
2014-11-25 06:11:17 1Xt7T8-0001mj-RD Completed

Drawbacks of this approach

  • If the former employee had multiple email addresses, every address must be listed.
  • The address remains in cached address books and suggested contacts for users who previously corresponded with it. After the mailbox is deleted, anyone who sends mail there receives a nondelivery response.