To provide access to remote DECnet MAIL and PSIMail via the local channel, versions of PMDF prior to version 3.2 used rewrite rules of the form

red.okstate.edu $U$%RED@yellow.okstate.edu green.okstate.edu PSI$%101202::$U@yellow.okstate.edu blue.okstate.edu $U$%BLUE@yellow.okstate.edu slate.okstate.edu $U$%GRAY@yellow.okstate.edu

or of the form

red.okstate.edu RED::$U@yellow.okstate.edu green.okstate.edu PSI$%101202::$U@yellow.okstate.edu blue.okstate.edu BLUE::$U@yellow.okstate.edu slate.okstate.edu GRAY::$U@yellow.okstate.edu

Here RED and BLUE are remote DECnet systems, GREEN is a remote PSIMail system, GRAY is a remote DECnet system whose domain name (slate.okstate.edu) differs from its DECnet node name, and YELLOW is the local host. This mechanism is still available in order to preserve compatability with earlier versions.

The problem with this scheme is that while these rewrite rules provide full access to the remote systems, they also rewrite addresses in message headers, resulting in undesirable header address formats.

Enhanced rewriting facilities introduced with PMDF V3.2 make it possible to avoid this problem and still provide the necessary access to remote systems. This is accomplished as follows:

1. Use the rewriting rules only to canonicalize addresses, that is, the rewrite rules convert all possible incoming addresses into the proper domain format addresses that should appear in the message headers.
2. Use the DECnet MAIL-11 channel (d channel) to provide access to remote DECnet systems. Use special MAIL channels to provide access to PSIMail.
3. Use appropriate channels in conjunction with channel-level translation operations (in the channel block) to map domain address back into DECnet MAIL or PSIMail addresses. If possible mark the channel with the 733 keyword and use domain names whose leftmost section (the part before the first period) corresponds to the DECnet MAIL or PSIMail system name in order to lessen the number of channel-level translation operations that are needed.

For example, the rewrite rules shown above could be implemented in PMDF with the following rewrite rules and channel blocks:

red.okstate.edu $U@RED.OKSTATE.EDU red $U@RED.OKSTATE.EDU green.okstate.edu $U@GREEN.OKSTATE.EDU green $U@GREEN.OKSTATE.EDU blue.okstate.edu $U@BLUE.OKSTATE.EDU blue $U@BLUE.OKSTATE.EDU slate.okstate.edu $U@SLATE.OKSTATE.EDU slate $U@SLATE.OKSTATE.EDU gray $U@SLATE.OKSTATE.EDU ... d DECNET-MAIL RED.OKSTATE.EDU RED BLUE.OKSTATE.EDU BLUE SLATE.OKSTATE.EDU GRAY mail_psi PSI-MAIL GREEN.OKSTATE.EDU 101202

Or, using the 733 keyword to simplify things somewhat:

red.okstate.edu $U%RED.OKSTATE.EDU@DECNET-MAIL red $U%RED.OKSTATE.EDU@DECNET-MAIL green.okstate.edu $U@GREEN.OKSTATE.EDU green $U@GREEN.OKSTATE.EDU blue.okstate.edu $U%BLUE.OKSTATE.EDU@DECNET-MAIL blue $U%BLUE.OKSTATE.EDU@DECNET-MAIL slate.okstate.edu $U@SLATE.OKSTATE.EDU slate $U@SLATE.OKSTATE.EDU gray $U@SLATE.OKSTATE.EDU ... d 733 DECNET-MAIL SLATE.OKSTATE.EDU GRAY mail_psi PSI-MAIL GREEN.OKSTATE.EDU 101202