Each delivery agent that is defined in the configuration file may or may not have an L= (line length) equate (L=). If that equate is missing, or if the value assigned to it is less than or equal to zero, and if the F=L delivery agent flag (F=L) is set, the default value that is used becomes the value of SMTPLINELIM. Otherwise, the default value is 0. This logic is there to support old configuration files that use F=L in place of the newer L=.

The default for SMTPLINELIM is 990 (defined in RFC821), and that value should not be changed. Rather, if you need a different line-length limit for a particular delivery agent, you should use the L= equate when defining it.