It is most safe to remove command mail entries from aliases. Another 2nd best solution follows: use_command_mail_function = no In this case, /usr/local/libexec/fml/command runs once but does not work and ends as soon as possible. The following solution may be possible. use_command_mail_function = yes command_mail_restrictions = reject When fml receives the incoming command mail, it inform the rejection to the sender in all cases. This configuration works but it evalutates each line. It is useless.