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Semantics of access_db

  • Database checked three times during transaction:

  • Connect: (Initial connection, before HELO/EHLO)
    From: (MAIL FROM:)
    To: (RCPT TO:)  (with blacklist_recipients)
  • Each check may involve several hash lookups
  • If relay_hosts_only not on, domains checked from specific to general; first match (if any) wins
  • Connect check can be postponed so that addresses are captured in logs
  • Records without "tags" are checked during all phases
  • RELAY is a superset of OK
  • DISCARD with To: silently discards message for specific recipient only