Bold Emails in Job Listings

You can try modifying your code as follows to correctly bold email addresses in job listings:

function bold_emails_in_job_listings($content) {
    if (is_singular('job_listing')) {
        $content = preg_replace_callback('/\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b/', function($matches) {
            return '<strong>' . $matches[0] . '</strong>';
        }, $content);
    }

    return $content;
}
add_filter('the_content', 'bold_emails_in_job_listings');

The change I made is in the regular expression pattern. I replaced [A-Z|a-z] with [A-Za-z] to correctly match email addresses in both uppercase and lowercase letters. This should make your function work as expected, and it will bold email addresses in job listings.