PMDF System Manager's Guide
2.2.3 Application of Domain Rewriting Rules to Addresses
This section presents a discussion of the operation of domain rewriting
rules: how an address is parsed and then transformed via rewrite rules.
This section touches briefly on the syntax of rewrite rules as such
syntax relates to example addresses, but for full details on rewrite
rule syntax, see Section 2.2.4 and Section 2.2.5 below.
There are four steps in the application of the domain rewriting rules
to a given address:
- The first host or domain specification is extracted from the
address. (Note that an address may specify more than one host or domain
name as is the case with the address firstname.lastname@example.org.)
- After extracting the first host or domain name specification, the
rewrite rules are scanned for a matching rewrite rule. That is, a
search is conducted for a rewrite rule whose pattern portion matches
the extracted host/domain name.
- Once a matching rewrite rule is found, the address is rewritten
according to the template portion of that rule. The template also
specifies the name of a routing system to which messages to this
address should be routed.7
- The routing system name is then compared with the host names
associated with each channel. If a match is found, then the message is
enqueued to that channel; otherwise, the rewriting process is
considered to have failed. If the matching channel is the local
channel, then some additional rewriting of the address may occur.
These four steps are described in detail in the following subsections.
There are also special template formats which allow for variations in
these four steps.
7 The term "routing system"
can be misleading. It does not necessarily mean the name of a system
through which the message will be routed but rather is a host name,
possibly fictitious, associated with a specific channel.