Sounds like this bug: Email header malformed when using SendMail
This is one of many acknowledged bugs that can be found in the Known Bug List here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html
Sounds similar. It looks like its been like this for sometime which is quite annoying.