Hi
I had the same problem.
Go here
C:\Program Files (x86)\Symantec\Symantec Endpoint Protection Manager\tomcat\etc\conf.properties
Add this line to the conf file, then all emails will be in normal text.
scm.email.content.type=text/plain
Restart server/service.
This works with single risk event, but some of them you will also have mht reports added.
Your single risk event mail size will also go down from 30kb to 3 kb.
Regards
Jimmie