One IP address (exclusively ours) among our email IPs at my place of employment was affected. We have used that IP for nine years. Emails are strictly transactional (receipts, password resets, et cetera).

The "rate limiting" started two weeks ago, giving us a code that Microsoft's documentation doesn't even list. It remains unresolved. Never had critical issues like this on our transactional IPs prior to this, and this particular IP address is still delivering just fine to other consumer and corporate email systems.