Tech Tip: Prevent all users from sending mail to a specific address

On occasion, you might want to prevent users from sending SMTP mail to a specific external address. For instance, perhaps your company wants to restrict employees from sending messages to certain mail lists or to a competitor's employment opportunities mail address.

While you can block inbound messages from specific addresses or entire domains with message filtering in the Exchange 5.5 Internet Mail Connector (IMC), there isn't a direct way to stop outbound messages from going to a specific address. However, you can work around this limitation.

Here's one way to do it:

  1. Create a custom recipient, assign it the SMTP address you wish to block, and click OK. (For this example, let's assume the SMTP address is
  2. Enter the SMTP address as the display name and alias for the custom recipient.
  3. Select the Delivery Restrictions tab, click List in the Accept Messages From pane, and click Modify.
  4. Select the custom recipient you created in Step 1, click Add, and click OK.
  5. Select the Advanced tab, select the Hide From Address Book check box, and click OK to close the dialog box.

Messages sent from your organization to the customer recipient you created in Step 1 will now return a nondelivery report similar to the following:

Your message did not reach some or all of the intended recipients.
Sent: 5/3/2003 8:53 AM
The following recipient(s) could not be reached: on 5/3/2003 8:53 AM
A restriction in the system prevented delivery of the message.

You can also use these procedures to allow or prevent any employees from sending to any SMTP address: Add more users in the Accept Messages From pane in Step 3, or select Reject Messages From and add users there.

The ability to add or remove users in Step 3 gives you a lot of flexibility in selecting who can send mail to a selected external SMTP address.

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