MASQUERADING AND RELAYING
You can have your host masquerade as another using
MASQUERADE_AS(`host.domain')
This causes mail being sent to be labeled as coming from the
indicated host.domain, rather than $j. One normally masquerades as
one of one's own subdomains (for example, it's unlikely that
Berkeley would choose to masquerade as an MIT site). This
behaviour is modified by a plethora of FEATUREs; in particular, see
masquerade_envelope, allmasquerade, limited_masquerade, and
masquerade_entire_domain.
The masquerade name is not normally canonified, so it is important
that it be your One True Name, that is, fully qualified and not a
CNAME. However, if you use a CNAME, the receiving side may canonify
it for you, so don't think you can cheat CNAME mapping this way.
Normally the only addresses that are masqueraded are those that come
from this host (that is, are either unqualified or in class {w}, the list
of local domain names). You can augment this list, which is realized
by class {M} using
MASQUERADE_DOMAIN(`otherhost.domain')
The effect of this is that although mail to user@otherhost.domain
will not be delivered locally, any mail including any user@otherhost.domain
will, when relayed, be rewritten to have the MASQUERADE_AS address.
This can be a space-separated list of names.
If these names are in a file, you can use
MASQUERADE_DOMAIN_FILE(`filename')
to read the list of names from the indicated file (i.e., to add
elements to class {M}).
To exempt hosts or subdomains from being masqueraded, you can use
MASQUERADE_EXCEPTION(`host.domain')
This can come handy if you want to masquerade a whole domain
except for one (or a few) host(s). If these names are in a file,
you can use
MASQUERADE_EXCEPTION_FILE(`filename')
Normally only header addresses are masqueraded. If you want to
masquerade the envelope as well, use
FEATURE(`masquerade_envelope')
There are always users that need to be "exposed" -- that is, their
internal site name should be displayed instead of the masquerade name.
Root is an example (which has been "exposed" by default prior to 8.10).
You can add users to this list using
EXPOSED_USER(`usernames')
This adds users to class {E}; you could also use
EXPOSED_USER_FILE(`filename')
You can also arrange to relay all unqualified names (that is, names
without @host) to a relay host. For example, if you have a central
email server, you might relay to that host so that users don't have
to have .forward files or aliases. You can do this using
define(`LOCAL_RELAY', `mailer:hostname')
The ``mailer:'' can be omitted, in which case the mailer defaults to
"relay". There are some user names that you don't want relayed, perhaps
because of local aliases. A common example is root, which may be
locally aliased. You can add entries to this list using
LOCAL_USER(`usernames')
This adds users to class {L}; you could also use
LOCAL_USER_FILE(`filename')
If you want all incoming mail sent to a centralized hub, as for a
shared /var/spool/mail scheme, use
define(`MAIL_HUB', `mailer:hostname')
Again, ``mailer:'' defaults to "relay". If you define both LOCAL_RELAY
and MAIL_HUB and you have FEATURE(`stickyhost'), unqualified names will
be sent to the LOCAL_RELAY and other local names will be sent to MAIL_HUB.
Note: there is a (long standing) bug which keeps this combination from
working for addresses of the form user+detail.
Names in class {L} will be delivered locally, so you must have aliases or
.forward files for them.
For example, if you are on machine mastodon.CS.Berkeley.EDU and you have
FEATURE(`stickyhost'), the following combinations of settings will have the
indicated effects:
| email sent to.... | eric | eric@mastodon.CS.Berkeley.EDU |
|---|
| LOCAL_RELAY set to | mail.CS.Berkeley.EDU | (delivered locally) |
| mail.CS.Berkeley.EDU | (no local aliasing) | (aliasing done) |
| MAIL_HUB set to | mammoth.CS.Berkeley.EDU | mammoth.CS.Berkeley.EDU |
| mammoth.CS.Berkeley.EDU | (aliasing done) | (aliasing done) |
| Both LOCAL_RELAY and | mail.CS.Berkeley.EDU | mammoth.CS.Berkeley.EDU |
| MAIL_HUB set as above | (no local aliasing) | (aliasing done) |
If you do not have FEATURE(`stickyhost') set, then LOCAL_RELAY and
MAIL_HUB act identically, with MAIL_HUB taking precedence.
If you want all outgoing mail to go to a central relay site, define
SMART_HOST as well.
Briefly:
- LOCAL_RELAY applies to unqualified names (e.g., "eric").
- MAIL_HUB applies to names qualified with the name of the
local host (e.g., "eric@mastodon.CS.Berkeley.EDU").
- SMART_HOST applies to names qualified with other hosts or
bracketed addresses (e.g., "eric@mastodon.CS.Berkeley.EDU"
or "eric@[127.0.0.1]").
However, beware that other relays (e.g., UUCP_RELAY, BITNET_RELAY,
DECNET_RELAY, and FAX_RELAY) take precedence over SMART_HOST, so if you
really want absolutely everything to go to a single central site you will
need to unset all the other relays -- or better yet, find or build a
minimal config file that does this.
For duplicate suppression to work properly, the host name is best
specified with a terminal dot:
define(`MAIL_HUB', `host.domain.')
note the trailing dot ---^
|