Thank you for contacting Windows Live Hotmail Domain Support. Your IP (xx.xx.xxx.xxx) was blocked by Windows Live Hotmail because the traffic/e-mail originating from your IP matched characteristics of recent spam attacks from compromised, or 'zombie' infected, machines.
After reviewing the information you provided, we have taken steps to remove the block. This change should take effect within the next 24-48 hours.
In order to prevent this and future exploits of this nature, please verify that your MTA's are under your full control, the MTA has not been compromised, and that you are not unwittingly sending any spam.
We also suggest that you scan your computer to verify that there is no malicious software installed. You can obtain a free Windows Server or client PC scan by visiting: http://safety.live.com (or) http://www.microsoft.com/athome/security/downloads/default.mspx
More information about this exploit can be found here: http://antivirus.about.com/od/whatisavirus/a/zombiepc.htm
We also reviewed your domain (xx.xx.xx) and could not find the presence of your SPF record(s). If you would like to receive the benefits of email authentication and validation, you need to create and add an SPF record for each domain. You can easily create your SPF record via our Sender-ID wizard located at http://www.microsoft.com/senderid/wizard Note this wizard provides flexibility to customize your records. To maximize compatibility and deliverability among receiving networks we strongly encourage you to NOT include a "PTR" record (as also discouraged by the IETF in RFC 4408), and to create a record optimized for BOTH the "Mail From" and the Purported Responsible Address, (PRA).
Once you have added the SPF record to your DNS it may take up to 2 business days to be fully replicated in the DNS and our systems. If you have any questions regarding this please let me know.
Additional information on common deliverability issues and best practices can be found on the Windows Live/Hotmail Postmaster Site found at: http://postmaster.live.com/. You may also want to review our "Improving E-mail Deliverability into MSN Hotmail and Windows Live Mail" downloadable document available at: http://www.microsoft.com/safety/postmaster.
The troubleshooting steps in this e-mail are recommendations only. Microsoft makes no guarantees that following these steps will guarantee deliverability to MSN, Hotmail, or Windows Live Mail customers.
Thank you for,
Windows Live Hotmail Domain Support