X-Mailer and headers when sending mail

Hi guys. When adding additional headers to an email that gets sent from the mail function. What purpose does the X-Mailer have? Also are the following linked: -X-Priority -Importance -X-MSMail-Priority Another question is can I omit the Message-ID for the email? or will this result in some mail servers viewing the mail as spam? What criteria do I use to generate the Message-ID? I've seen: $headers .= "Message-ID: <".date("YmdHis")."you@".$_SERVER['SERVER_NAME'].">\n"; is this ok? Perhaps if someone has a link on the headers for a mail that could help me it would be much appreciated. Thanks in advance -- Angelo Zanetti Z Logic www.zlogic.co.za [c] +27 72 441 3355 [t] +27 21 469 1052 [f] +27 86 681 5885