The cause: we believe that our project became so popular so Ford, as one of biggest Microsoft clients, asked Microsoft to block us
If seriously, the real cause is unknown as Microsoft doesn't explain it. But we believe that it may be caused by the free license emails sends that are quite numerous. Current status: we have tightened the mail server and DNS settings, and started to use external mail relay. Now the mails are delivered to Microsoft domains, but drop into the Spam/Junk folder. So, the problem is solved but only partially. Considering all the circumstances, the Microsoft domains will remain blocked on our server for free license and forum registrations. Only paid licenses and support requests will be processed from/to the Microsoft domains .
Conclusion: it seems the global E-Mail system slowly becomes another victim of this "free" World, so we have to implement other, more reliable methods of FORScan content delivery.
Request to FORScan users: if you expect any email from FORScan server, please also check in the Spam and Junk folders. This recommendation is actual for any mail domains (not only Microsoft ones).