This is the php session identifier. Are you using one of the template pages for your message? These pages are designed to print out all of the posted elements, so if you have one that is posting like this it will show in the email message.
I can take a look at your files and try to add something in for you that would suppress this value from getting into the message. Please post back with the page that has UE in it along with the webassist folder from your site in a zip archive.