We are also seeing this issue on rare occasions. But I did not suspect Cutesoft. Sometimes it ends up in a footer we append that part of the email is not generated by CuteSoft. Here is part of an offending email in yellow as an example output, note the ! should not be there.
Peachtree-Du! nwoody Road
You could try the suggestions in the posts on this page http://www.systemwebmail.com/faq/4.4.5.aspx
Jason