Mail::Mailer allows you to set the type of mail server you are using. It checks mailx, Mail and mail in that order if you do not specify the $type. So, in other words to change this default behavior from mailx Mail and mail to smtp a snippet might look like:

use Mail::Mailer;
use Mail::Mailer qw(mail);
$mailer = new Mail::Mailer;
$mailer = new Mail::Mailer 'smtp', Server => $server;
$mailer->open(\%headers);
print $mailer $body;
$mailer->close;
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