When an incoming email is fetched, an ASCII copy of each message is created and stored on disk in a separate file. The location of these copies is recorded in the ezsurvey.log. The form typically looks like:
Copying response from INBOX to W:\ezsurv\1.TXT
Each filename is a number followed by a .TXT extension. The most recent file will have the highest number. Look through the filenames to find which one may belong to the unprocessed email. It may also help to use a Windows Explorer directory listing showing the dates and times that files were accessed.