directory channel is similar in function to the alias
file. The alias file is only used when the addressee is on the local
system, or matches a channel marked with the
channel keyword, while the
directory channel provides
aliasing for other systems or
pseudo domains which your
system manages. The
directory channel also provides
facilities for looking up aliases using mechanisms other than a PMDF
directory channel is used to set up pseudo domains ---
systems which exist only in a logical sense. A
channel is used to transform the mailbox names associated with such a
pseudo domain into mailboxes on real systems. Such a scheme can be used
to standardize naming conventions for groups of disparate systems.
The directory channel includes special handling for subaddresses, akin to that for the local channel; see Section 22.214.171.124 and Section 126.96.36.199.
The transformations applied by the directory channel can be derived from a number of different information sources:
PMDF CRDB(OpenVMS) or
pmdf crdb(UNIX or NT) utility.
X.500look ups can be used, with a separate set of defaults for each pseudo domain.
CCSO/qi/phlook ups can be used, with a separate set of defaults for each pseudo domain.
Note that with appropriate use of the
keyword, the alias database can be used to implement functionality
similar to the directory channel's
crdb database type of
lookup on arbitrary pseudo domains. Similarly $(text) rewrite
rule substitutions and the PMDF general database6 can be
used to implement similar functionality. Such alias database or general
database use avoids the overhead of additional channel processing
incurred by the directory channel. But although such schemes may be
more efficient than using a
directory channel, the
crdb lookups do have some
additional features such as support of duplicate usernames, support of
alternate postmaster return addresses, and better diagnostic messages
when illegal addresses are used.
6 On OpenVMS, the logical