There are potentially hundreds or more tests run by a system such as Hotmail along the way that help determine if you email would be blocked, delivered to spam, or delivered to inbox. A single keyword such a doctor wouldn't be a single cause for an email to be blocked. Some initial checks include researching your outgoing IP address reputation and verifying you don't have any broken SPF records. How did your email fail? Was it blocked with a specific error message by Hotmail? Was it delivered to the spam folder?