When Verify Recipient Address is enabled on MS Exchange server, all emails are rejected

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By default, Microsoft Exchange servers will not verify the recipient. With an Microsoft Exchange server as the MTA, it is recommended to configure the FortiMail to use LDAP to do recipient verification using the Microsoft Active Directory service. Alternatively, you can configure Microsoft Exchange to enable SMTP recipient verification.

To configure recipient verification on a Microsoft Exchange server

1. Open the Microsoft Exchange system manager and go to Global settings > Message Delivery > Properties.
2. Select Recipient Filtering.
3. Select Filter recipients who are not in the Directory.
4. Go to Administrative Groups > First Administrative Group > Servers > [your server]> SMTP > the default SMTP virtual server > Properties.
5. Select Advanced.
6. Select Edit.
7. Select Apply Recipient Filter.
8. Select OK.
   

To test the configuration, telnet to port 25 of your Microsoft Exchange server.