Due to overzealous filtering on Microsoft’s side, some emails to Outlook and Hotmail addresses may not be delivered. If you’re affected, please use a different email address or try again later.
Exactly right.
PSA to the pub; Windows Defender will flag anything with "suspicious" code as a Wacatac. That's basically what it defaults to when it doesn't know what an application or link-library does (or doesn't want to find out what it does.)