This article contains supportability information on Messaging Gateway and its support for Perfect Forward Secrecy on TLS conversations
Symantec has added support for PFS in SMG 10.5.3. Please update at your earliest convenience to take advantage of this feature. SMG 10.5.3 is available via the Updates page by clicking the "Check for updates" button if you have not received notification of it's availability.
Please contact support if you have further questions.