FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
The FortiGate SMTP Signature can be added to incoming AND/OR outgoing email (done with different Protection Profiles on the incoming vs. outgoing Firewall Policy). If the signature is enabled on incoming email, attachment behavoir may be modified.
This problem has been reported with Exchange 5.5 SMTP servers, but not with Exchange 2000 or 2003.
The FortiGate unit adds the Signature as a multipart MIME attachment, and this creates an additional multipart/mixed boundary nesting layer. Exchange 5.5 can interpret these in such a way, that the received email will contain an empty body (or just the signaure), and an attachment. This attachment will then contain further attachments with itself. All of the original email content will be available, but presented in this odd manner.
