Aliases have multiple uses with e-mail. Individual users
typically use aliases as abbreviations. For instance, rather
than remember John Doe's full e-mail address, an alias JD can
be created so that mail sent to the address JD is properly sent
using John Doe's full address (e.g., JD573@VAXC.EXAMPLE.COM).
System managers often use aliases in order to create valid mail
addresses for non-existent users. For instance, an alias named
Postmaster might be created and equated with the username SYSTEM
so that incoming network mail for the user Postmaster is routed
to the SYSTEM account. These are just two examples of the many
practical uses of aliases.
The process of interpreting an alias is called "alias expansion".
In the two examples above, the aliases JD and Postmaster expand,
respectively, to JD573@VAXC.EXAMPLE.COM and SYSTEM.
In this documentation, the expansion of an alias is represented
with the following notation
alias-name - > alias-value
For example, John - > JD573@VAXC.EXAMPLE.COM.
PMDF alias names are "case insensitive". This means that the
alias names jd, JD, jD, and Jd are all considered to be identical
by PMDF; the case (upper versus lower case) of the individual
characters in an alias name is irrelevant to PMDF. However, PMDF
does preserve the case of alias values.
PMDF aliases can expand to:
- an address: JD - > JD573@VAXC.EXAMPLE.COM,
- a list of addresses: STAFF - >
BOB@EXAMPLE.COM,SUE@EXAMPLE.COM,
- other aliases: JD - > JOHND - > JD573@VAXC.EXAMPLE.COM,
- a list of aliases: COMPANY - > STAFF,ADMIN,FACULTY, or
- a mixture of addresses and aliases: LIST - >
STAFF,BOB@EXAMPLE.COM.
Note that in the above example, it is not clear whether or not
the expanded value of an alias is another alias or not; i.e.,
in "JD - > JOHND", JOHND could have been either an alias or
a legitimate username. PMDF always starts by assuming that an
address without any domain part (e.g., @EXAMPLE.COM) is an alias
and attempts to expand it. When expanding an alias, PMDF first
tries to look up the alias in the user's personal alias database
and, if the alias is not found there, then PMDF consults system-
level alias sources. After expanding an alias once, PMDF then
tries to expand the result (or results in the case of a list).
This expansion process is repeated until no more expansions are
possible at which point the results are all assumed to be real
mail addresses and not aliases.
By default, alias names can be from 1 to 80 characters long and
their expansion values 0 to 252 characters. This corresponds
to a "long" alias database file which is the type of file DB
normally creates. When a "huge" alias database file is used, the
maximum lengths of the alias names and their expansion values
are, respectively, 80 and 1024 characters. When a "short" alias
database file is used, the maximum lengths of the alias names and
their expansion values are, respectively, 32 and 80 characters.
Note that by default the system alias database created with the
CRDB utility is a short alias database.
When specifying mail addresses within VMS MAIL or DECwindows
MAIL, PMDF aliases must be specified using the format IN%alias-
name. For example, mail addressed as follows
MAIL> SEND
To: IN%JD
would use PMDF's alias for JD, if any exists. From PMDF MAIL, you
can simply use JD rather than IN%JD.
System managers can find it useful to establish forwarding for
commonly used system wide aliases. For example,
MAIL> SET FORWARD/USER=POSTMASTER IN%Postmaster
with Postmaster a PMDF alias (in the system alias database) which
points to the user or users who should receive mail intended for
the system's postmaster. When this type of forwarding has been
set up, users can then just send mail to the (fictitious) user
POSTMASTER,
MAIL> SEND
To: POSTMASTER
and PMDF will route it to the proper individuals.