The check_ Rule Sets

V8.8 sendmail has introduced a suite of named rule sets that have special internal meaning. If one of these rule sets does not exist, the address is accepted. If it exists and if the rule set returns anything other than an #error delivery agent, the message is accepted. Otherwise the message is rejected.

• check_compat
• Compares or contrasts each envelope sender and envelope recipient pair of addresses just before delivery, and validates based on the result. The workspace looks like this:
  
  

  sender $| recipient
  

  The sender address is separated from the recipient address by a single token that is the $| operator (see §29.10.4).

• check_mail
• Validates the sender-envelope address as given in the SMTP MAIL command. The workspace, on entry, contains a hostname that should be preprocessed by rule set 3 (see §29.10.1).
• check_rcpt
• Validates the recipient-envelope address as given in the SMTP RCPT command. The workspace, on entry, contains a hostname that should be preprocessed by rule set 3 (see §29.10.2).
• check_relay
• Validates incoming network connections and can be used if libwrap.a code was omitted from your release of sendmail. The workspace looks like this:
  
  

  hostname $| IPnumber
  

  The hostname is separated from the IP number by a single token that is the $| operator (see §29.10.3).