Each time an address that matches the local channel¹ or any
channel marked with the aliaslocal keyword is encountered
by PMDF's message submission logic, the mailbox (e.g.,
username) specified in the address is compared against each entry in
the alias database or alias file. Additionally, if the PMDF options
LDAP_HOST, LDAP_PORT, and one or more of ALIAS_URL0, ALIAS_URL1, ALIAS_URL2, or
ALIAS_URL3 are specified in the PMDF option file (see Section 7.3.2 ),
then the mailbox specified in the address is used to generate an LDAP
query. The LDAP query, if any, is performed after the regular alias
file and alias database queries. If a match occurs the alias address is
replaced by the translation value or values specified by the alias. An
alias can translate into any combination and number of additional
aliases or real addresses. (Note that in the case of an LDAP query,
multiple addresses may be returned both if the LDAP query matches
multiple entries containing a desired attribute(s), or if the LDAP
query matches a multivalued attribute of a single entry.) The real
addresses need not themselves be associated with the local channel and
thus aliases can be used to forward mail to remote systems. If the
translation value of an alias is a file name preceded by a <, then
the contents of that file are used as a mailing list (e.g.,
distribution list) and the message is sent to each recipient listed in
the file; if the translation value of an alias is an LDAP URL preceded
by a < that returns one or multiple addresses, then the message is
sent to each address returned. This process is occasionally referred to
as "mail exploding". See Section 4.1 for directions on how
to set up a mailing list.
Aliases only apply to addresses mapped to the local channel¹ or to
channels marked with the aliaslocal keyword; furthermore,
note that since the only addresses truly considered to match a channel
are Envelope To: addresses, aliases can only apply to Envelope To:
addresses. PMDF performs alias translation and expansion only after
address parsing is completed. The translation values produced by an
alias are treated as completely new addresses and are reprocessed from
scratch.²
Aliases as well as mailing lists, a special case of an alias, may be
tested with the command PMDF TEST/REWRITE/CHECK_EXPANSIONS (OpenVMS) or
pmdf test -rewrite -check_expansions (UNIX or NT). See for
details. For LDAP lookups of incoming addresses matching the local
channel, see Section 3.1.1 . Also, in regards to mailing lists, see
the final part of Section 4.1.3 .