Many Unix mail-reading programs, such as /usr/ucb/Mail, require that each mail message in a file of many mail messages be delimited from the others by a blank line, then a line that begins with the five characters "From ":

and thanks again. -- bill            one message ends
                                     a blank line
From george Fri Dec 13 12:03:45 2002 next message starts

This means that any given mail message can have only one line in it that begins with the five characters "From ". To prevent such lines from being improperly fed to such mail delivery agents, sendmail offers the F=E delivery agent flag. This delivery agent flag tells sendmail to insert a > character at the front of all but the first such lines found. Consider the following:

From tim@here.us.edu Fri Dec 13 13:00:03 2002

From now on, let's meet on Saturdays instead of Tuesdays,
like we discussed.

If the F=E delivery agent flag is specified for the delivery agent that delivers the preceding message, sendmail converts it to read:

From tim@here.us.edu Sat Dec 14 13:00:03 2002

>From now on, let's meet on Saturdays instead of Tuesdays,
like we discussed.

This F=E delivery agent flag is rarely needed, and is only routinely included with the *file* delivery agent. Usually, the program specified by the local delivery agent definition handles From line conversions. This delivery agent flag should be used only with delivery agents that handle final local delivery.