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Postfix Documentation
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To rewrite message headers or not, or to label as invalid

Postfix versions 2.1 and earlier always rewrite message header addresses, and append Postfix's own domain information to addresses that Postfix considers incomplete. While rewriting message header addresses is OK for mail with a local origin, it is undesirable for remote mail:

  • Message header address rewriting is frowned upon by mail standards,
  • Appending Postfix's own domain produces incorrect results with some incomplete addresses,
  • Appending Postfix's own domain sometimes creates the appearance that spam is sent by local users.

Postfix versions 2.2 give you the option to either not rewrite message headers from remote SMTP clients at all, or to label incomplete addresses in such message headers as invalid. Here is how it works:

  • Postfix always rewrites message headers from local SMTP clients and from the Postfix sendmail command, and appends its own domain to incomplete addresses. The local_header_rewrite_clients parameter controls what SMTP clients Postfix considers local (by default, only local network interface addresses).
  • Postfix never rewrites message header addresses from remote SMTP clients when the remote_header_rewrite_domain parameter value is empty (the default setting).
  • Otherwise, Postfix rewrites message headers from remote SMTP clients, and appends the remote_header_rewrite_domain value to incomplete addresses. This feature can be used to append a reserved domain such as "domain.invalid", so that incomplete addresses cannot be mistaken for local addresses.
Postfix Documentation
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