Email rejections - Hotmail, Outlook & Live.com

We're currently experiencing some deliverability issues to Microsoft-hosted email addresses (i.e. Hotmail, Outlook & Live.com). This is due to Microsoft taking issue with the IP addresses used by our email service provider, who is working to resolve the situation. As a result of this our systems have automatically and temporarily paused sending email to those addresses. Organisations impacted by this will have sent email on the 25th, 26th, or 27th. Email addresses which are showing as Rejected as a result of this should be lifted automatically after about 3 days; many already are.