Address direction and location-specific rewrites

Address direction and location-specific rewrites, $B, $E, $F, $R
It is sometimes useful to specify rewrite rules that only apply to envelope addresses or, alternately, only apply to header addresses. The control sequence   forces a rewrite to fail if the address being  rewritten is not an envelope address. The control sequence   forces a  rewrite to fail if the address being rewritten is not from the message  header or body. These sequences have no other effects on the rewrite and may appear anywhere in the rewrite rule template.

Addresses may also be categorized by direction. A forward-pointing address is an envelope To address or an address  that originates on a To:, Cc:, Resent-To:, or other  header line that refers to a destination. A backwards-pointing address is an envelope From address or an address from a header line such as From:, Sender:, or Resent-From:, referring to a source. The control sequence   causes  the rewrite to fail if the address is backwards-pointing. The control sequence   causes the rewrite to fail if the address is  forward-pointing.

The first of the following rewrite rules causes forward pointing envelope addresses (i.e., envelope To addresses) of the form user@oldhost.domain.com to  be rewritten to user@newhost.domain.com and the message routed to the    channel: oldhost.domain.com    $U%newhost.domain.com@tcp_intranet-daemon$E$F oldhost.domain.com    $U@domain.com All other, non-envelope-To occurrences, of addresses of the form user@oldhost.domain.com are rewritten to  user@domain.com by the second rewrite rule.

See also:
 * Rewrite rule template substitutions and control sequences