The sendmail.cf HoldExpensive option (HoldExpensive) tells sendmail not to connect to expensive delivery agents. Instead, mail destined for those agents is queued for later delivery. This F=e delivery agent flag marks a delivery agent as expensive.

For example, consider a site connected to the Internet over a dial-on-demand ISDN link that costs lots of money per minute. Such a site might want all the Internet mail to be queued and would arrange for that queue to be processed only once every other hour.

Under V8 sendmail, verbose output (watch delivery) cancels the effect of the F=e delivery agent flag (suppresses queueing).^[29] Verbose output is set with the -v command-line switch (-v) or the Verbose option (Verbose).

^[29] According to Eric Allman, "It's assumed that if you say you want to watch delivery, you really want to watch it."