+# Returns the local Fully Qualified Domain Name (FQDN) if available.
+#
+# Tightly configured MTAa require that a caller sends a real DNS
+# domain name that corresponds the IP address in the HELO/EHLO
+# handshake. This is used to verify the connection and prevent
+# spammers from trying to hide their identity. If the DNS and IP don't
+# match, the receiveing MTA may deny the connection.
+#
+# Here is a deny example of Net::SMTP with the default "localhost.localdomain"
+#
+# Net::SMTP=GLOB(0x267ec28)>>> EHLO localhost.localdomain
+# Net::SMTP=GLOB(0x267ec28)<<< 550 EHLO argument does not match calling host
+#
+# This maildomain*() code is based on ideas in Perl library Test::Reporter
+# /usr/share/perl5/Test/Reporter/Mail/Util.pm ==> sub _maildomain ()
+
+sub valid_fqdn {
+ my $domain = shift;
+ return !($^O eq 'darwin' && $domain =~ /\.local$/) && $domain =~ /\./;
+}
+
+sub maildomain_net {
+ my $maildomain;
+
+ if (eval { require Net::Domain; 1 }) {
+ my $domain = Net::Domain::domainname();
+ $maildomain = $domain if valid_fqdn($domain);
+ }
+
+ return $maildomain;
+}
+
+sub maildomain_mta {
+ my $maildomain;
+
+ if (eval { require Net::SMTP; 1 }) {
+ for my $host (qw(mailhost localhost)) {
+ my $smtp = Net::SMTP->new($host);
+ if (defined $smtp) {
+ my $domain = $smtp->domain;
+ $smtp->quit;
+
+ $maildomain = $domain if valid_fqdn($domain);
+
+ last if $maildomain;
+ }
+ }
+ }
+
+ return $maildomain;
+}
+
+sub maildomain {
+ return maildomain_net() || maildomain_mta() || 'localhost.localdomain';
+}
+