Grumble. Trying to send e-mail to a hotmail user

All evening long I've been fighting with trying to get mail sent from slimy.com (or leonardfamilytutoring.com) to a hotmail address and failing. It keeps sending bounce messages like this:

This is the mail system at host phantom.slimy.com.

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

<name-here@hotmail.com>: host mx4.hotmail.com[65.55.37.120] said: 550 SC-001
Mail rejected by Windows Live Hotmail for policy reasons. Reasons for
rejection may be related to content with spam-like characteristics or
IP/domain reputation problems. If you are not an email/network admin please
contact your E-mail/Internet Service Provider for help. Email/network
admins, please visit http://postmaster.live.com for email delivery
information and support (in reply to MAIL FROM command)

[-- Attachment #2: Delivery report --]
[-- Type: message/delivery-status, Encoding: 7bit, Size: 0.7K --]

Reporting-MTA: dns; phantom.slimy.com
X-Postfix-Queue-ID: 4464681CA
X-Postfix-Sender: rfc822; beth@oasis.slimy.com
Arrival-Date: Mon, 7 Dec 2009 08:13:26 +0000 (UTC)

Final-Recipient: rfc822; shannon_o@hotmail.com
Original-Recipient: rfc822;shannon_o@hotmail.com
Action: failed
Status: 5.0.0
Remote-MTA: dns; mx4.hotmail.com
Diagnostic-Code: smtp; 550 SC-001 Mail rejected by Windows Live Hotmail for
policy reasons. Reasons for rejection may be related to content with
spam-like characteristics or IP/domain reputation problems. If you are not
an email/network admin please contact your E-mail/Internet Service Provider
for help. Email/network admins, please visit http://postmaster.live.com for
email delivery information and support

[-- Attachment #3: Undelivered Message --]
[-- Type: message/rfc822, Encoding: 7bit, Size: 2.9K --]

...

When I send the message to gmail, it winds up in my spam the first time I use an address, but if I move it out, subsequent messages get through just fine. We added the spf stuff MS wants, and it shows up in gmail as "pass" so I don't know what else to try.

Received-SPF: pass (google.com: domain of beth@oasis.slimy.com designates 74.82.3.76 as permitted sender) client-ip=74.82.3.76;
Authentication-Results: mx.google.com; spf=pass (google.com: domain of beth@oasis.slimy.com designates 74.82.3.76 as permitted sender) smtp.mail=beth@oasis.slimy.com

Help me O internet friends, you're my only hope!
--Beth