I want to suggest a little change about the saving of the preferences. I think it's better to use the UserId instead of the Email address. Also the folder where the images are stored by default should be named after the userid instead of the email address.
This can be simply done by changing two lines.
code:
ss4.preferences.js (54): sMyRegPath = sTmp + Messenger.myUserId;
ss4.preferences.js (216): sPath+='\\Screenshot Sender\\'+Messenger.MyUserId+'\\';