Problem
When recipient verification is enabled on the Microsoft Exchange server, all email is rejected.
Solution
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. Enable Recipient Filtering.
3. Click 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. Click Advanced.
6. Click Edit.
7. Click Apply Recipient Filter.
8. Click OK.
To test the configuration, open a Telnet connection to port 25 of your Microsoft Exchange server.