After sending a mass email and viewing the email preview while logged in as different user, the details of the current user appear on the email not the details of the user that created the original email.
The email template that is used contains the #user_firstname# and #user_lastname# merge fields.
Once the merge is carried out on a group these fields should be popluated with the user who carried out the mass email.
But if another user logs in and views these emails their details appear on the email not the details of the user who sent it.
This issue is currently with development and will be fixed in a future version of Sage CRM.