Sending alerts with in-line HTML or alternatives

We’d like to send email alerts with findings for specific machines to the system owner. We can programmatically do it via OMP. Ideally, the alerts would have an HTML report filtered for the specific system displayed in-line in the email. Unfortunately, the in-line HTML is always displayed as HTML code rather than rendered in HTML. Has anyone seen this behavior and possibly know of a way to get the in-line HTML to work?

Content-type set correctly?