Symantec Mail Security for Domino 8.x exits with an error "Unknown OS error" when multiple mailboxes are enabled on Domino server and the parameter "Mail_Enable_Mailbox_Compatibility=1" is added to notes.ini.
When Symantec Mail Security for Domino 8.x exits, the error "Unknown OS error" is reported on the Domino server console.
When multiple mailboxes are enabled, they are titled mail1.box, mail2.box and so on. The parameter "Mail_Enable_Mailbox_Compatibility=1" in notes.ini is used to force the router to use mail.box instead of mail1.box. When set, this parameter keeps the "Mail.box" file and creates mail2.box, mail3.box and so on.
In this scenario, the nntask of Symantec Mail Security for Domino 8.x fails to load with "Unknown OS Error" when mail1.box is missing.
The issue is fixed in the Symantec Mail Security for Domino (SMSDOM) 126.96.36.199.
To work around this behavior without upgrading to SMSDOM 188.8.131.52, please do one or more of the following, then restart the Domino server to make changes effective:
The affected environment found so far appears to be Domino Server 8.5.1/FP1(32bit), Windows 2003 Server 32bit and Symantec Mail Security for Domino 8.0.5/8.0.6