public-inbox-mda: use <sysexits.h> status codes where applicable

Many MTA understand these and map them to sensible SMTP error messages.

Inability to find an inbox results in "5.1.1 user unknown".
Misformatted messages are rejected with "5.6.0 data format error".
Unsupported inbox versions are reported as "5.3.5 local configuration error".

All of these are interpreted as permanent failures.

diff --git a/script/public-inbox-mda b/script/public-inbox-mda
index 766d58a6f4c22cd97ca91a9fda6dc7bd421d8bca..1f1252a7a8bc240e631adb863cb5cb84ec39ed92 100755 (executable)
--- a/script/public-inbox-mda
+++ b/script/public-inbox-mda
@@ -38,8 +38,8 @@ my $config = PublicInbox::Config->new;
 my $recipient = $ENV{ORIGINAL_RECIPIENT};
 defined $recipient or die "ORIGINAL_RECIPIENT not defined in ENV\n";
 my $dst = $config->lookup($recipient); # first check
-defined $dst or do_exit(1);
-my $main_repo = $dst->{mainrepo} or do_exit(1);
+defined $dst or do_exit(67); # EX_NOUSER 5.1.1 user unknown
+my $main_repo = $dst->{mainrepo} or do_exit(67);
 
 # pre-check, MDA has stricter rules than an importer might;
 do_exit(0) unless PublicInbox::MDA->precheck($simple, $dst->{address});
@@ -73,7 +73,7 @@ if (ref($ret) && $ret->isa('Email::MIME')) { # filter altered message
 } elsif ($ret == PublicInbox::Filter::Base::IGNORE) {
        do_exit(0); # chuck it to emergency
 } elsif ($ret == PublicInbox::Filter::Base::REJECT) {
-       $! = $ret;
+       $! = 65; # EX_DATAERR 5.6.0 data format error
        die $filter->err, "\n";
 } # else { accept
 
@@ -88,6 +88,7 @@ if ($v == 2) {
        my $git = $dst->git;
        $im = PublicInbox::Import->new($git, $dst->{name}, $recipient, $dst);
 } else {
+       $! = 78; # EX_CONFIG 5.3.5 local configuration error
        die "Unsupported inbox version: $v\n";
 }
 if (defined $im->add($mime)) {