Threat Prevention Mail Configuration

What can I do here?

In this window you can configure how Threat Prevention and Anti-Virus scan emails.

Getting Here - Security Policies > Threat Prevention > Policy > Threat Tools > Profiles > Profile > Mail > MIME Nesting

Maximum MIME nesting level is (levels) - Set the maximum number of levels that will be scanned in a MIME email with nested contents. This controls how deeply into the nesting the ThreatSpect engine will scan.
When nesting level is exceeded (action on file) - If there are more MIME nested levels in an email than the maximum configured level, you can configure to block or allow the file.