Known to apply to the following Sophos product(s) and version(s)
Astaro Security Gateway/Sophos UTM
V7, V8, V9
What To Do
When using Sophos's Mail Security sub-system, the SMTP Proxy can validate every incoming message's recipient address against the mail server.
Recipient verification will prevent non-delivery reports/bounce messages for non-existent email addresses on the recipient's email domain.
1. In the Sophos's webadmin portal, go to Email Protection > SMTP > Routing
Under Recipient Verification Section set 'Verify Recipients' to 'with callout (recommended)'. Click on the 'Apply' button
2. On the Lotus Domino Server, go to Router/SMTP > Restrictions and Controls 'Verify that local domain recipients exist in the Domino Directory' Set to 'Enabled'.
The Lotus Domino Server will now reject invalid addresses back to the UTM which will terminate the connection to the remote mail server.