7.5.2.5 SKIP
This keyword provides a way to list hosts, domains, or addresses that can give a
default behavior. Such defaults are defined by your selection of features to enable.
Sometimes, for example, you might desire to have the lookup of a host, domain, or
address return (if found), but have no further checks performed on it. One way to do
that is by using this special SKIP keyword as the return value for the lookup:
From:bob.domain SKIP
If the lookup was done to see whether relaying is OK for the domain bob.domain,
this SKIP instructs sendmail to act as though the lookup did not find bob.domain.
Thus, if the default is to deny relaying, relaying for bob.domain will be denied. If the
default is to allow relaying, relaying for bob.domain will be allowed.
The main use for SKIP is with the FEATURE(lookupdotdomain) (?§17.8.26 on page 628).
With that feature defined, you could set up the access database like this:
From:server.bob.domain SKIP
From:.bob.domain RELAY
Here, mail from the machine server.bob.domain will be handled by the default rules.
All other hosts in the bob.domain domain will be allowed to relay.
7.5.2.6 XYZ text
The SMTP protocol, as documented in RFC2821, defines a set of three-digit codes
that have special meaning to the sending site. When sendmail rejects the envelope
sender, it does so by printing a 550 code in reply to the MAIL From: command.
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