When using Symantec Encryption Desktop (SED) with an IMAP account and Outlook 2013 (64-bit), sent emails are stored as "Draft Messages" (i.e. they are editable) in the Sent folder.
This issue is fixed in the Symantec Encryption 10.4/3.4 release, which was made available on June 2016.
Applies To
Outlook 2013 (64bit), SED 10.3.x