it's been that way since 2003 when somebody complained about
smtp as default (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=152729);
That issue was about submitting using smtpd versus directly to sendmail.
Using the nmh sendmail/smtp mts would invoke sendmail directly, as
requested, simply using the smtp protocol.
sendmail/pipe uses sendmail -t, which causes sendmail to read the
addresses from the draft. Its sole purpose is to replace the obsolete and
undocumented mh spost. I don't think that sendmail/pipe offers any
advantage here over sendmail/smtp, and has the disadvantage that
sendmail/pipe does not support Dcc:.
Re. sendmail/pipe, are these comments in post.c still valid?
/* This won't work with MTS_SENDMAIL_PIPE. */
verify_all_addresses (1, eai, envelope, oauth_flag, auth_svc);
as far as i can tell yes, because verify_all_addresses uses do_an_address
uses sm_wadr which talks smtp.
Right, so verify_all_addresses() does work when the user has specified
sendmail/pipe, though it uses sendmail/smtp, in effect, here. I'll update
personally i think spending any further effort on verifying addresses for
deliverability on the sending side is wasted because of how little
verification/guarantee it provides (see bugs section in man whom).
Good point. I find "whom -check" to be useless or even misleading.