Please read the following article about a new wave of Cryptolockers currently in the wild (Trojan.Cryptolocker.G and Trojan.Cryptolocker.E especially). This article includes a tip on how to use SEP's ADC component to increase your security.
Support Perspective: CTB-Locker and other forms of Crypto malware
https://www-secure.symantec.com/connect/blogs/support-perspective-ctb-locker-and-other-forms-crypto-malware
I also recommend ensuring that mail servers are using the latest definitions. It would be a good idea to apply Rapid Release defs to SMSMSE and other products protecting mail servers a couple times per day. This will improve detection of the very latest Downloaders (usually Downloader.Ponik) that are used to deliver the ultimate cryptolocking payload.
Virus Definition Update Methods Available for Symantec Mail Security for Microsoft Exchange (SMSMSE)
http://www.symantec.com/docs/TECH131756
Many thanks!
Mick