Wont send to hotmail?

[nullsystems]

I can send email to gmail, domains hosted on this server and others. But not hotmail. Any ideas why?

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Hi. This is the qmail-send program at mydomainhosting.com.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<xxx@hotmail.com>:
Connected to 65.54.245.104 but sender was rejected.
Remote host said: 550 Command rejected for policy reasons. For troubleshooting information, go to http://postmaster.msn.com

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Revised: I believe hotmail blocked the domain, any ideas on if they remove automatically?