The L= delivery agent equate is used to limit the length of text lines in the body of a mail message. If this equate is omitted and if the delivery agent has the obsolete F=L delivery agent flag set (F=L), sendmail defaults to SMTPLINELIM (990) as defined in conf.h (SMTPLINELIM). If the F=L is clear (as it is in modern configuration files), sendmail defaults to 0 (which means an unlimited line length). The F=L is honored for compatibility with older versions of sendmail that lack this L= delivery agent equate.

Limiting line length causes overly long lines to be split. When an output line is split, the text up to the split is first transmitted, followed by the ! character. After that, the characters defined by the E= delivery agent equate are transmitted. A line can be split into two or more pieces. For example, consider the following text from the body of a mail message:

The maximum line length for SMTP mail is 990 characters.
A delivery agent speaks SMTP when the $u sendmail macro
is omitted from the A= equate.

A delivery agent could limit line length to 20 characters with a declaration of:


With that limit, the preceding text would be split during transmission into the following lines:

The maximum line len!
gth for SMTP mail is!
990 characters.
A delivery agent spe!
aks SMTP when the $u!
sendmail macro
is omitted from the !
A= equate.

Limiting the line length can be useful for programs that can’t handle long lines, such as a 40-character braille print-driving program. ...

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