In theory it is supported (https://www.symantec.com/docs/TECH236572), but I can't tell you how it would work for email encryption.
Most likely for an unamanaged SED Client, every user that logs onto the box will be capable of sending emails, so you'd probably want a SEMS to manage SED and control who can and who cannot use Email Encryption.
Not tested any of this BTW, and it's all just off the top of my head so I'd recommend having a play with the software.