gistfile1.php

<?php

function mailer($smtpHost) {
    return function($from, $to, $subject, $content) use ($smtpHost) {
        mail(...);
    };
}

$myMailer = mailer('smtp.google.com');

$myMailer('leounglaub@whatever.com', 'xat@whatever.com', 'was geht?', 'blah');