Hello I have been following this tutorial: "The Perfect Server – Debian Lenny (Debian 5.0) With BIND & Dovecot [ISPConfig 3]" Everything works fine except when I try to send mails to a hotmail account. I get this fault repport: (I use of course postfix) ////////////////////////////////////////////////////////////////////////////////////////////////////////// This is the mail system at host server1.xxxxxxxxx.dk. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system <email@example.com>: host mx4.hotmail.com[126.96.36.199] said: 550 SC-001 Unfortunately, messages from 188.8.131.52 weren't sent. Please contact your Internet service provider since part of their network is on our block list. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. (in reply to MAIL FROM command) ///////////////////////////////////////////////////////////////////////////////////////////////////// I understand that it is something with Id-sender, but nothing more but that. Does somebody knows what i have to do?