What steps can be taken to troubleshoot and resolve issues with special characters being removed from email subject lines in PHP scripts?

Special characters may be removed from email subject lines in PHP scripts due to encoding issues. To resolve this, you can use the `mb_encode_mimeheader()` function to properly encode the subject line with the appropriate character set.

$subject = "Subject with special characters é, ñ, ü";
$subject = mb_encode_mimeheader($subject, "UTF-8", "Q");