🚀 go-pugleaf

In article <1992Nov6.104509.16949@hp4at.eunet.co.at> optkap@hp4at.eunet.co.at (Hochleitner) writes:
>I am very interested in the relation between mail and sendmail.

There are actually several different programs called 'mail', and there are
other programs (elm, mush are examples) which do something similar.

>It is clear to me, that mail is the Ua, which enables better user interface, 
>and sendmail is the Tma, who is responsible for the delivery of the mail.

The user agent, say /usr/ucb/mail, prepares the message, then pipes it
in /usr/lib/sendmail -oi address address ...

Sendmail fills in any remaining headers, determines how it should be
routed, and attempts to deliver it to the next host on the route.  If the
mail is for a local user, sendmail pipes it to the local delivery agent,
commonly /bin/mail.

>I meen the process communication between mail and sendmail (only the pipe is
>not enough).

Usually there is just the pipe and the parameter list.  The important
part of the parameter list is the list of recipient addresses.   There
is usually a '-oi' which means that the message should not terminate at
the first '.', and there may be one or two other options.

>             ANother important question in this field is, how sendmail
>fills its "standard macros" like $g, $w and ohters, because not all these
>macros are set explicitly in the sendmail.cf file.

$w is set by first using gethostname(), then using that as an argument
to gethostbyname().  If you are using a nameserver, the result should
be the fully qualified domain name of your host.  If you are not using
a nameserver, possible the value of gethostname() will be used, or the
first entry on the line in /etc/hosts which matches this name.  If
necessary you can actually override this with a 'Dw' line in the
configuration file.

$g is the address after processing by the rewrite rules.  The sender address
is processed by rulesets 3,1, S=, 4  [where S= is the ruleset named on the
"S=" operand of the outbound mailer].