Microsoft has recently revealed that it now uses Certified Senders Alliance (CSA) to get more information when they need additional data regarding a questionable sender which generated complaints from their users but not enough to be categorized as bad.
Here are the cases where Microsoft uses CSA data:
a) We regularly see spam complaints from bulk senders that are on the CSA list, and so they contact the folks at Eco asking them to look into that particular sender. Visibility for reputation list providers is important.
b) We also take the CSA reputation list into consideration when a sender has delivery trouble at Outlook.com; if they are on the list, it means they’ve gone through the steps of trying to be a good sender.
c) And finally, we recommend that one path senders can take if they want to improve their deliverability in general is to join the CSA because it will help with sending email to various places around the Internet, not just Outlook.com, because if you follow those steps then it reduces the chances that you will display behavior that is considered abusive.
The whole blog post can be seen here.