Hello,
as the current "db_sub.tpl" contains all host entries the "db.tpl" also consists, the "20_named_dualstack.pl" in line 116 should be extended from for my $name('@', 'ftp') { to for my $name('@', 'ftp', 'mail', 'imap', 'pop', 'pop3', 'relay', 'smtp') {.
Regards Jörg