sendmail, 4th Edition

F=| (vertical bar)

Check for |program addresses V8.7 and later

Prior to V8.7 sendmail, only the local delivery agent could recognize the | character as a directive to pipe the mail message through a program (see Delivery Via Programs on page 468 and Piping Through Programs on page 504).

Beginning with V8.7, any delivery agent can be made to accept the leading | character. If the F=| delivery agent flag is present, the delivery agent will accept the leading | character and call the prog delivery agent to pipe the message through a program. If the delivery agent flag is absent, this ability to pipe is prohibited. In general, the F=| delivery agent flag should be present for the local and local-clone delivery agents but absent for all others. In configuration files prior to version 6 (The V Configuration Command on page 580), this delivery agent flag is automatically set for the local delivery agent.

This delivery agent flag is legal only for addresses contained in ~/.forward files or aliases(5) databases. Any |program address in an SMTP dialog or on the command line will be rejected.