The five character "From " that begins a line is used to separate one message from another in a user's mailbox (See this section). This is a convention used by some but not all MUAs. The "From " line is generated by mail.local when it delivers the message. Its form looks like this:

From user@host.domain Fri Dec  13 09:10:40 2002

The user is ordinarily determined by getting the login name of the user who ran mail.local with the getlogin(3) routine. If that lookup fails, mail.local gets the name of the user from the passwd(5) file that is associated with the uid of the user that ran mail.local. If that fails, it sets the username to "???."

This -f command-line switch allows you to override the envelope sender's user identity. For example:

define(`LOCAL_MAILER_ARGS', `mail.local -f sysmail@our.domain DOL(u)')

Here, we first omit declaration of the local_lmtp feature, to prevent local LMTP delivery. We then force the envelope sender name, as it appears in the "From " line of delivered mail, to appear as though it is from the user sysmail, by using this -f command-line switch.

Note that the envelope sender is the address to which failed mail is bounced. It is not the address used for replies.

Also note that when mail.local receives email with LMTP it gathers the actual envelope sender address from the MAIL FROM: command and places that address in the "From " line. When that happens this -f command-line switch is ignored.