Symantec Mail Security for Microsoft Exchange (SMSMSE) quarantines some compressed files (.zip, .rar or other format) that are attached to email messages. The compressed files are marked "unscannable."
This problem can occur when the uncompressed size of the file contents exceeds the maximum total size limit that is configured in Symantec Mail Security.
In Symantec Mail Security 5.0 for Microsoft Exchange or above, you can adjust the attachment size limits in the SMSMSE user interface.
To modify the attachment size limits in Symantec Mail Security 4.x for Microsoft Exchange, change the values of the following registry keys:
The value is the largest file size (in bytes) that you want to permit. Any files that extract to a larger size than you specify are quarantined as unscannable files.