Some Unix mailbox formats require a blank line at the end of one message and before the start of the next message. If your local version of /bin/mail does not assure that this blank line exists, you can use the F=b delivery agent flag. If this delivery agent flag is specified and if the message being sent to the delivery agent lacks a blank line at the end, sendmail adds one. This delivery agent flag is also appropriate for use with the *file* delivery agent.