Fn

F=n

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Don't use Unix-style From in header

All versions

The Unix-style mailbox (a single file into which many mail messages are placed) requires that each message be separated from the others by a blank line, followed by 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  

Ordinarily, sendmail adds a five-character " From " line to a message if there isn't one. The F=n delivery agent flag prevents sendmail from doing this. It is intended for use when not dealing with a Unix-style mailbox, or when dealing with a delivery agent that adds the blank line and " From " by itself.

Note that if the F=U delivery agent flag is specified (but not F=n ), the five-character UUCP-style " From " header line is created, and the words remote from $g are appended to that line. The F=n delivery agent flag should always be specified for SMTP delivery agents . The five-character " From " line is not a valid RFC2822 header (because it lacks a colon ) and is not permitted.

Apart from SMTP, the use of the F=n delivery agent flag is best determined on a case-by-case basis. Some delivery agents always generate a " From " line, so the F=n delivery agent flag can be used to avoid duplication. Some delivery agents generate a " From " line only if there is not already one there, so the F=n delivery agent flag is optional and perhaps best omitted. Some delivery agents never generate a " From " line, yet require one (such as the uux program); for these the F=n delivery agent flag should always be omitted.