Okay, I see your point here: your server is able to send mail without issue via SquirrelMail. Unfortunately, I don't know enough about SquirrelMail to know what method, exactly, it uses to do so. It would seem that it uses a method that differs from standard SMTP, as evidenced by the fact that sending mail via SquirrelMail functions as expected. Maybe SquirrelMail uses some PHP method to send mail that bypasses Postfix altogether, hence no problems. I don't know why you are receiving a 404 during that process, but that issue seems to be unrelated. You didn't answer my question. Have you tried sending mail to recipients at domains other than live.com? The reason I ask is that all of the failures in your log (at least within the sample that you provided) are @live.com, using the mail delivery server mx1.hotmail.com. It is possible that live.com / hotmail.com is blocking these connections from your server. Also, based on this post of yours ( http://www.howtoforge.com/forums/showpost.php?p=270463&postcount=2 ), as Till said, either: a.) the ports in question are closed on your server, or b.) the services are not running on the ports that you think they are, or c.) connections to the ports are being blocked by a firewall. I realize that you are convinced that this is not the case, but logic dictates as much. What happens when you issue the following command from your server's terminal: Code: traceroute mx1.hotmail.com ?