This is best shown by example. Consider the network shown in Figure 42-1 . A snads_local channel would connect the PMDF-XGS system apollo.olympus.org with the SNADS world, handing off messages to the SNADS node APPLE, by way of the PMDF-XGS transport bridge AMBROSIA.
Figure 42-1 Sample SNADS and SMTP site
On the PMDF side, one would add MX records for pseudodomain names such as apple.olympus.org, cherry.olympus.org, banana.olympus.org, and damson.olympus.org pointing to the PMDF-XGS system apollo.olympus.org.
On the SNADS side, one would at a minimum configure the SNADS nodes APPLE, CHERRY, BANANA, and DAMSON to believe that the PMDF-XGS transport bridge AMBROSIA is another SNADS node, and that APOLLO is another SNADS node reachable through AMBROSIA. One would probably also configure the SNADS nodes to believe that CUPID, BACCHUS, and DIANA are additional SNADS nodes reachable through AMBROSIA.
That is, on the SMTP side, the SNADS nodes APPLE, CHERRY, BANANA and DAMSON would appear to be additional SMTP systems apple.olympus.org, cherry.olympus.org, banana.olympus.org, and damson.olympus.org reachable through apollo.olympus.org; on the SNADS side, the SMTP systems apollo.olympus.org, cupid.olympus.org, bacchus.olympus.org, and diana.olympus.org would appear to be additional SNADS nodes APOLLO, CUPID, BACCHUS, and DIANA reachable through the AMBROSIA transport bridge in its guise of SNADS node.
Then using the standard naming conventions, user carol at cupid.olympus.org can address a user CHARLES at CHERRY as charles@cherry.olympus.org (or perhaps even as charles@cherry, if the TCP/IP package and PMDF system are configured to allow use of short form names). User BOB at BANANA can address mail to betty at bacchus.olympus.org as BETTY@BACCHUS, but will not be able to address christopher at cupid directly, because SNADS names are limited to eight characters. This is solved by sending the mail to the PMDF addressing channel by addressing the mail to MAILMAN@APOLLO, and embedding the addresses of the real recipients in the text of the note. This also applies to recipients at SMTP hosts for which PMDF has not been configured to convert the short form host name into a fully qualified domain name, or whose host name is over eight characters long. For instance a SNADS user could not directly address priscilla at prometheus, or susan@styx.hades.org.