Host Lookups

Host alias entries may take one of the following forms:

host		new_host
host		sender_host:recipient_host
host		sender_host:recipient_host:envelope_host

Mailer table entries may take one of the following forms:

host		local:
host		error:error message
host		mailer:relay
host		mailer:relay:new_host

In the lookup order tables below, ~___ represents one of the following
user types:

~STA		addresses that you might want to stay here (eg, root)
~INC		:include: addresses
~PRC		process (pipe) addresses
~LDS		file addresses (leading slash but not X.400)
~EMS		addresses with embedded (but not leading) slashes
~X4		X.400 addresses (/$*=$*/)
~REG		all other ("regular") addresses

----------------------------------------------------------------------
For "host.domN.dom1" where host.domN.dom1 is the local host ("this host"):

host.domN.dom1.~___.~THH
host.domN.dom1.~THH
.domN.dom1.~___.~THH		%1 = host; %2 = domN.dom1.~___.~THH
.domN.dom1.~THH			%1 = host; %2 = domN.dom1.~THH
	.				.
	.				.
	.				.
.dom1.~___.~THH			%1 = host.domN; %2 = dom1.~___.~THH
.dom1.~THH			%1 = host.domN; %2 = dom1.~THH
.~___.~THH			%1 = host.domN.dom1; %2 = ~___.~THH
.~THH				%1 = host.domN.dom1; %2 = ~THH

If none of these lookups succeed, the "no host" cases are also tried.

----------------------------------------------------------------------
For a non-local address via the local host (eg, the host portion refers to
the local host, but the user portion contains a '!', '@', or '%') where
the local host is host.domN.dom1:

host.domN.dom1.~VIA
.domN.dom1.~VIA			%1 = host; %2 = domN.dom1.~VIA
	.				.
	.				.
	.				.
.dom1.~VIA			%1 = host.domN; %2 = dom1.~VIA
.~VIA				%1 = host.domN.dom1; %2 = ~VIA

----------------------------------------------------------------------
For "[a.b.c.d]" where [a.b.c.d] is a domain literal for the local host:

[a.b.c.d].~___.~THH
[a.b.c.d].~THH
.~ADR.~___.~THH			%1 = [a.b.c.d]; %2 = ~___.~THH
.~ADR.~THH			%1 = [a.b.c.d]; %2 = ~___.~THH
.~___.~THH			%1 = [a.b.c.d]; %2 = ~___.~THH
.~THH				%1 = [a.b.c.d]; %2 = ~THH

----------------------------------------------------------------------
For "[a.b.c.d]" where [a.b.c.d] is a domain literal:

[a.b.c.d]
?.~ADR				%1 = [a.b.c.d]; %2 = ~ADR (if host is unknown)
.~ADR				%1 = [a.b.c.d]; %2 = ~ADR (known or unknown)

----------------------------------------------------------------------
For an address with no host part:

~___.~NOH
.~NOH				%1 = ~___; %2 = ~NOH

----------------------------------------------------------------------
For a UUCP host:

host.UUCP
host				(host alias only)
?.UUCP				%1 = host; %2 = UUCP (if host is unknown)
.UUCP				%1 = host; %2 = UUCP (known or unknown)

----------------------------------------------------------------------
For a fully-qualified host part:

host.domN.dom1
?.domN.dom1			%1 = host; %2 = domN.dom1 (if host is unknown)
.domN.dom1			%1 = host; %2 = domN.dom1 (known or unknown)
	.				.
	.				.
	.				.
?.dom1				%1 = host.domN; %2 = dom1 (if unknown)
.dom1				%1 = host.domN; %2 = dom1
?.~FQD				%1 = host.domN.dom1; %2 = ~FQD (if unknown)
.~FQD				%1 = host.domN.dom1; %2 = ~FQD

----------------------------------------------------------------------
For an unqualified host part:

host
?.~HST				%1 = host; %2 = ~HST (if host is unknown)
.~HST				%1 = host; %2 = ~HST (known or unknown)