postfix can not send to a hotmail account

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

<nevernis@hotmail.dk>: host mx4.hotmail.com[65.55.37.88] said: 550 SC-001
Unfortunately, messages from 78.47.226.154 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?

 

As mentioned in the Hotmail's reply:

So you will need to contact your ISP, and ask them to contact hotmail to get the block removed from the Hotmail's block list.

It will/should help if you give your ISP the link that is in the Hotmail's reply: http://mail.live.com/mail/troubleshooting.aspx#errors, and tell them that it's about SMTP Error code: 550 SC-001

Code 550 SC-001 reads:

Basically spam is beening send from the IP block that you are on.

After this you will need to setup the needed reverse DNS and SPF record for your domain(s)

 

ok, thank you