Ugh
sendmail is a pain to configure. I mean, have you seen a sendmail.cf file recently? I don't know how it could be made any easier, but there's gotta be a better way. (Actually, qmail makes for a nice sendmail replacement.)
(Here's a piece that is responsible for forwarding email to virtual hosted domains:)
# handle virtual usersSure-- that's pretty obvious...
R$+ < @ $=w . > $: < $(virtuser $1 @ $2 $@ $1 $: @ $) > $1 < @ $2 . >
R<@> $+ + $* < @ $* . >
$: < $(virtuser $1 + * @ $3 $@ $1 $: @ $) > $1 + $2 < @ $3 . >
R<@> $+ + $* < @ $* . >
$: < $(virtuser $1 @ $3 $@ $1 $: @ $) > $1 + $2 < @ $3 . >
R<@> $+ < @ $+ . > $: < $(virtuser @ $2 $@ $1 $: @ $) > $1 < @ $2 . >
R<@> $+ $: $1
R< error : $- $+ > $* $#error $@ $(dequote $1 $) $: $2
R< $+ > $+ < @ $+ > $: $>97 $1