10.9.3.1 The FORWARD Mapping Table

The FORWARD mapping table provides this functionality of pattern based forwarding, and also provides a mechanism for source specific forwarding. If a FORWARD mapping table exists in the mapping file, it is applied to each envelope To: address. No changes are made if this mapping does not exist or no entries in the mapping match.

If the address matches a mapping entry, the result of the mapping is tested. The resulting string will replace the envelope To: address if the entry specifies a $Y; a $N will discard the result of the mapping. See Table 10–8 for a list of additional flags.

Table 10–8 FORWARD Output Mapping Table Flags Description

Flag	Description
$D	Run output through the rewriting process again
$G	Run output through the forward lookup table, if forward lookup table use has been enabled
$H	Disable further forward lookup table or FORWARD mapping lookups
$I	Hold the message as a .HELD file
$N	Address remains unchanged
$Y	Use output as new address

The FORWARD mapping, if present, is consulted before any forward lookup table lookup. If a FORWARD mapping matches and has the flag $G, then the result of the FORWARD mapping will be checked against the forward lookup table, if forward lookup table use has been enabled via the appropriate setting of USE_FORWARD_DATABASE. (Note that if channel specific forward lookup table use has been specified, then the source address and source channel will be prefixed to the result of the FORWARD mapping before looking up in the forward lookup table.) If a matching FORWARD mapping entry specifies $D, then the result of the FORWARD mapping (and optional forward table lookup) will be run through the MTA address rewriting process again. If a matching FORWARD mapping entry specifies $H, then no further FORWARD mapping or database lookups will be performed during that subsequent address rewriting (that resulting from the use of $D).

The following input flags are now available in the FORWARD mapping. In the past they were only available to the various *_ACCESS mappings.

Table 10–9 FORWARD Input Mapping Table Flags Description

Flag	Description
$A	SASL used to authenticate connection.
$D	NOTIFY=DELAYS active for this recipient.
$E	Incoming connection used ESMTP/EHLO.
$F	NOTIFY=FAILURES active for this recipient.
$L	Incoming connection used LMTP/LHLO.
$S	NOTIFY=SUCCESSES active for this recipient.
$T	SSL/TLS used to secure connection.

The example below illustrates the use of a complex REVERSE and FORWARD mapping. Suppose that a system or pseudo domain named am.sigurd.innosoft.com associated with the mr_local channel produces RFC 822 addresses of the general form:

"lastname, firstname"@am.sigurd.example.com

or

"lastname,firstname"@am.sigurd.example.com

Although these addresses are perfectly legal they often confuse other mailers which do not fully comply with RFC 822 syntax rules—mailers which do not handle quoted addresses properly, for instance. Consequently, an address format which does not require quoting tends to operate with more mailers. One such format is

firstname.lastname@am.sigurd.example.com

Example of a complex FORWARD and REVERSE mapping:

REVERSE

 *|mr_local|"*,$ *"@am.sigurd.example.com $Y"$1,$ $2"@am.sigurd.example.com
 *|mr_local|"*,*"@am.sigurd.example.com   $Y"$1,$ $2"@am.sigurd.example.com
 *|*|"*,$ *"@am.sigurd.example.com        $Y$3.$2@am.sigurd.example.com
 *|*|"*,*"@am.sigurd.example.com          $Y$3.$2@am.sigurd.example.com
 *|mr_local|*.*@am.sigurd.example.com     $Y"$2,$ $1"@am.sigurd.example.com
 *|*|*.*@am.sigurd.example.com            $Y$2.$3@am.sigurd.example.com

FORWARD

 "*,$ *"@am.sigurd.example.com            $Y"$0,$ $1"@am.sigurd.example.com
 "*,*"@am.sigurd.example.com              $Y"$0,$ $1"@am.sigurd.example.com
 *.*@am.sigurd.example.com                $Y"$1,$ $0"@am.sigurd.example.com

So the goals of the sample mapping tables in the above example are threefold. (1) Allow any of these three address formats above to be used. (2) Present only addresses in the original format to the mr_local channel, converting formats as necessary. (3) Present only addresses in the new unquoted format to all other channels, converting formats as necessary. (The REVERSE mapping shown assumes that bit 3 in the MTA option USE_REVERSE_DATABASE is set.