Check the mcebuddy.conf file, the relevant section in mine looks like:
eMailSuccessSubject=MCEBuddy - Success - %originalfilename%
eMailFailedSubject=MCEBuddy - FAILED - %originalfilename%
eMailCancelledSubject=
eMailStartSubject=MCEBuddy Start %originalfilename% -%taskname%
eMailDownloadFailedSubject=
eMailSuccessSubject=MCEBuddy - Success - %originalfilename%
eMailFailedSubject=MCEBuddy - FAILED - %originalfilename%
eMailCancelledSubject=
eMailStartSubject=MCEBuddy Start %originalfilename% -%taskname%
eMailDownloadFailedSubject=