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早期freebsd实现

nocanonify	Don't pass addresses to $[ ... $] for canonification.
		This would generally only be used by sites that only
		act as mail gateways or which have user agents that do
		full canonification themselves.  You may also want to
		use "define(`confBIND_OPTS',`-DNSRCH -DEFNAMES')" to
		turn off the usual resolver options that do a similar
		thing.

notsticky	By default, email sent to "[e-mail]" are marked
		as "sticky" -- that is, the local addresses aren't
		matched against UDB and don't go through ruleset 5.
		This features disables this treatment.  It would
		normally be used on network gateway machines.

mailertable	Include a "mailer table" which can be used to override
		routing for particular domains.  The argument of the
		FEATURE may be the key definition.  If none is specified,
		the definition used is:
			hash -o /etc/mailertable
		Keys in this database are fully qualified domain names
		or partial domains preceded by a dot -- for example,
		"vangogh.CS.Berkeley.EDU" or ".CS.Berkeley.EDU".
		Values must be of the form:
			mailer:domain
		where "mailer" is the internal mailer name, and "domain"
		is where to send the message.  These maps are not
		reflected into the message header.

domaintable	Include a "domain table" which can be used to provide
		full domains on unqualified (single word) hosts.  The
		argument of the FEATURE may be the key definition.  If
		none is specified, the definition used is:
			hash -o /etc/domaintable
		The key in this table is the unqualified host name; the
		value is the fully qualified domain.  Anything in the
		domaintable is reflected into headers; that is, this
		is done in ruleset 3.

bitdomain	Look up bitnet hosts in a table to try to turn them into
		internet addresses.  The table can be built using the
		bitdomain program contributed by John Gardiner Myers.
		The argument of the FEATURE may be the key definition; if
		none is specified, the definition used is:
			hash -o /etc/bitdomain.db
		Keys are the bitnet hostname; values are the corresponding
		internet hostname.

uucpdomain	Similar feature for UUCP hosts.  The default map definition
		is:
			hash -o /etc/uudomain.db
		At the moment there is no automagic tool to build this
		database.

always_add_domain
		Include the local host domain even on locally delivered
		mail.  Normally it is not added unless it is already
		present.

allmasquerade	If masquerading is enabled (using MASQUERADE_AS), this
		feature will cause recipient addresses to also masquerade
		as being from the masquerade host.  Normally they get
		the local hostname.  Although this may be right for
		ordinary users, it can break local aliases.  For example,
		if you send to "localalias", the originating sendmail will
		find that alias and send to all members, but send the
		message with "To: localalias@masqueradehost".  Since that
		alias likely does not exist, replies will fail.  Use this
		feature ONLY if you can guarantee that the ENTIRE
		namespace on your masquerade host supersets all the
		local entries.

nodns		We aren't running DNS at our site (for example,
		we are UUCP-only connected).  It's hard to consider
		this a "feature", but hey, it had to go somewhere.

nullclient	This is a special case -- it creates a stripped down
		configuration file containing nothing but support for
		forwarding all mail to a central hub via a local
		SMTP-based network.  The argument is the name of that
		hub.
		
		The only other feature that should be used in conjunction
		with this one is "nocanonify" (this causes addresses to
		be sent unqualified via the SMTP connection; normally
		they are qualifed with the masquerade name, which
		defaults to the name of the hub machine).  No mailers
		should be defined.  No aliasing or forwarding is done.


+-------+
| HACKS |
+-------+

Some things just can't be called features.  To make this clear,
they go in the hack subdirectory and are referenced using the HACK
macro.  These will tend to be site-dependent.  The release
includes the Berkeley-dependent "cssubdomain" hack (that makes
sendmail accept local names in either Berkeley.EDU or CS.Berkeley.EDU;
this is intended as a short-term aid while we move hosts into
subdomains.


+--------------------+
| SITE CONFIGURATION |
+--------------------+

Complex sites will need more local configuration information, such as
lists of UUCP hosts they speak with directly.  This can get a bit more
tricky.  For an example of a "complex" site, see cf/ucbvax.mc.

If your host is known by several different names, you need to augment
the $=w class.  This is a list of names by which you are known, and
anything sent to an address using a host name in this list will be
treated as local mail.  You can do this in two ways: either create
the file /etc/sendmail.cw containing a list of your aliases (one per
line), and use ``FEATURE(use_cw_file)'' in the .mc file, or add the
line:

	Cw alias.host.name

at the end of that file.  See the ``vangogh.mc'' file for an example.
Be sure you use the fully-qualified name of the host, rather than a
short name.

The SITECONFIG macro allows you to indirectly reference site-dependent
configuration information stored in the siteconfig subdirectory.  For
example, the line

	SITECONFIG(uucp.ucbvax, ucbvax, U)

reads the file uucp.ucbvax for local connection information.  The
second parameter is the local name (in this case just "ucbvax" since
it is locally connected, and hence a UUCP hostname).  The third
parameter is the name of both a macro to store the local name (in
this case, $U) and the name of the class (e.g., $=U) in which to store
the host information read from the file.  Another SITECONFIG line reads

	SITECONFIG(uucp.ucbarpa, ucbarpa.Berkeley.EDU, W)

This says that the file uucp.ucbarpa contains the list of UUCP sites
connected to ucbarpa.Berkeley.EDU.  The $=W class will be used to
store this list, and $W is defined to be ucbarpa.Berkeley.EDU, that
is, the name of the relay to which the hosts listed in uucp.ucbarpa
are connected.  [The machine ucbarpa is gone now, but I've left
this out-of-date configuration file around to demonstrate how you
might do this.]

Note that the case of SITECONFIG with a third parameter of ``U'' is
special; the second parameter is assumed to be the UUCP name of the
local site, rather than the name of a remote site, and the UUCP name
is entered into $=w (the list of local hostnames) as $U.UUCP.

The siteconfig file (e.g., siteconfig/uucp.ucbvax.m4) contains nothing
more than a sequence of SITE macros describing connectivity.  For
example:

	SITE(cnmat)
	SITE(sgi olympus)

The second example demonstrates that you can use two names on the
same line; these are usually aliases for the same host (or are at
least in the same company).


+--------------------+
| USING UUCP MAILERS |
+--------------------+

It's hard to get UUCP mailers right because of the extremely ad hoc
nature of UUCP addressing.  These config files are really designed
for domain-based addressing, even for UUCP sites.

There are four UUCP mailers available.  The choice of which one to
use is partly a matter of local preferences and what is running at
the other end of your UUCP connection.  Unlike good protocols that
define what will go over the wire, UUCP uses the policy that you
should do what is right for the other end; if they change, you have
to change.  This makes it hard to do the right thing, and discourages
people from updating their software.  In general, if you can avoid
UUCP, please do.

The major choice is whether to go for a domainized scheme or a
non-domainized scheme.  This depends entirely on what the other
end will recognize.  If at all possible, you should encourage the
other end to go to a domain-based system -- non-domainized addresses
don't work entirely properly.

The four mailers are:

    uucp-old (obsolete name: "uucp")
	This is the oldest, the worst (but the closest to UUCP) way of
	sending messages accros UUCP connections.  It does bangify
	everything and prepends $U (your UUCP name) to the sender's
	address (which can already be a bang path itself).  It can
	only send to one address at a time, so it spends a lot of
	time copying duplicates of messages.  Avoid this if at all
	possible.

    uucp-new (obsolete name: "suucp")
	The same as above, except that it assumes that in one rmail
	command you can specify several recipients.  It still has a
	lot of other problems.

    uucp-dom
	This UUCP mailer keeps everything as domain addresses.
	Basically, it uses the SMTP mailer rewriting rules.

	Unfortunately, a lot of UUCP mailer transport agents require
	bangified addresses in the envelope, although you can use
	domain-based addresses in the message header.  (The envelope
	shows up as the From_ line on UNIX mail.)  So....

    uucp-uudom
	This is a cross between uucp-new (for the envelope addresses)
	and uucp-dom (for the header addresses).  It bangifies the
	envelope sender (From_ line in messages) without adding the
	local hostname, unless there is no host name on the address
	at all (e.g., "wolf") or the host component is a UUCP host name
	instead of a domain name ("somehost!wolf" instead of
	"some.dom.ain!wolf").

Examples:

We are on host grasp.insa-lyon.fr (UUCP host name "grasp").  The
following summarizes the sender rewriting for various mailers.

Mailer          sender		rewriting in the envelope
------		------		-------------------------
uucp-{old,new}	wolf		grasp!wolf
uucp-dom	wolf		[e-mail]
uucp-uudom	wolf		grasp.insa-lyon.fr!wolf

uucp-{old,new}	[e-mail]	grasp!fr.net!wolf
uucp-dom	[e-mail]	[e-mail]
uucp-uudom	[e-mail]	fr.net!wolf

uucp-{old,new}	somehost!wolf	grasp!somehost!wolf
uucp-dom	somehost!wolf	somehost![e-mail]
uucp-uudom	somehost!wolf	grasp.insa-lyon.fr!somehost!wolf

If you are using one of the domainized UUCP mailers, you really want
to convert all UUCP addresses to domain format -- otherwise, it will
do it for you (and probably not the way you expected).  For example,
if you have the address foo!bar!baz (and you are not sending to foo),
the heuristics will add the @uucp.relay.name or @local.host.name to
this address.  However, if you map foo to foo.host.name first, it
will not add the local hostname.  You can do this using the uucpdomain
feature.


+-------------------+
| TWEAKING RULESETS |
+-------------------+

For more complex configurations, you can define special rules.
The macro LOCAL_RULE_3 introduces rules that are used in canonicalizing
the names.  Any modifications made here are reflected in the header.

A common use is to convert old UUCP addreses to SMTP addresses using
the UUCPSMTP macro.  For example:

	LOCAL_RULE_3
	UUCPSMTP(decvax,	decvax.dec.com)
	UUCPSMTP(research,	research.att.com)

will cause addresses of the form "decvax!user" and "research!user"
to be converted to "[e-mail]" and "[e-mail]"
respectively.

This could also be used to look up hosts in a database map:

	LOCAL_RULE_3
	R$* < @ $+ > $*		$: $1 < @ $(hostmap $2 $) > $3

This map would be defined in the LOCAL_CONFIG portion, as shown below.

Similarly, LOCAL_RULE_0 can be used to introduce new parsing rules.
For example, new rules are needed to parse hostnames that you accept
via MX records.  For example, you might have:

	LOCAL_RULE_0
	R$+ <@ host.dom.ain.>	$#uucp $@ cnmat $: $1 < @ host.dom.ain.>

You would use this if you had installed an MX record for cnmat.Berkeley.EDU
pointing at this host; this rule catches the message and forwards it on
using UUCP.

You can also tweak rulesets 1 and 2 using LOCAL_RULE_1 and LOCAL_RULE_2.
These rulesets are normally empty.

A similar macro is LOCAL_CONFIG.  This introduces lines added after the
boilerplate option setting but before rulesets, and can be used to
declare local database maps or whatever.  For example:

	LOCAL_CONFIG
	Khostmap hash /etc/hostmap.db
	Kyplocal nis -m hosts.byname


+---------------------------+
| MASQUERADING AND RELAYING |
+---------------------------+

You can have your host masquerade as another using

	MASQUERADE_AS(host.domain)

This causes outgoing SMTP mail to be labeled as coming from the
indicated domain, rather than $j.  One normally masquerades as one