This article contains information on the possible reasons for which e-mails are piling up in the "mail.box" Domino router file when Symantec Mail Security for Domino (SMSDOM) is installed on the server.
Every time SMSDOM scans a mail that's been handled by the Domino Router process, it will place the email in a "Scan Pending" status in the mail.box router file, and then will hand the file to the scanning process.
Once a verdict is given by SMSDOM (and mail ahs been cleaned from violations, if found), the mail is then released for delivery from the router file.
An excessivly long "Scan Pending" status can be caused by one or more of the following items:
SMSDOM Container Limits set too high (Settings > Configuration > Scan Error > Container Limits)
The recommended maximum value is "20".
Higher values may help this problem occur.
SMSDOM scan threads (notes.ini parameter)
Mail and Write SMSDOM scan threads may be increased in number to allow more room for scanning messages.