I received this back from Microsoft:

Conditionally mitigated
74.208.227.221

Our investigation has determined that the above IP(s) qualify for conditional mitigation. These IP(s) have been unblocked, but may be subject to low daily email limits until they have established a good reputation. Please note that mitigating this issue does not guarantee that your email will be delivered to a user’s inbox. Ongoing complaints from users will result in removal of the mitigation. Mitigation may take 24 - 48 hours to replicate completely throughout our system. If you feel your issue is not yet resolved, please reply to this email and one of our support team members will contact you for further investigation.