sendmail, 4th Edition

Further Processing: $:address

The address part of the triple is intended for use in the command line of the delivery agent and in the RCPT command in an SMTP connection. For either use, that address is rewritten by rule set 2 (if there is one), the R= equate of the delivery agent, and the final rule set 4, as illustrated in Figure 19-5. This means that the address part can be in focused form because the focus is later removed by the final rule set 4. But the address part must be a single username (no host) for some local delivery agents.

The rewritten result is stored for use when a delivery agent’s $u in A= (A= on page 738) argument is expanded. For example, for the local delivery agent, the rewritten result is the username as it will be given to /bin/mail for local delivery.

Figure 19-5. The flow of $:address through rule sets

The rewritten result is also given to a remote site during the exchange of mail using the SMTP protocol. The local machine tells the remote machine the name of the recipient by saying RCPT To: followed by the rewritten address portion of the triple.