Hi Tony,
Thanks so much for getting back to us. We've got a great link to share with you that has some more information about the different email account types:
email account types
Are you currently able to send and receive new emails in the Mail app?
Since you're seeing messages from before 2016, let's see if we can take a step to verify if messages after 2016 are still available on your email server. Many email service providers have a website you can sign into to view your email online through your web browser. If you're aware of such a website, let us know if you see newer email messages in the inbox when you sign into the website directly.
If you're not sure if your email service provider offers web access, we recommend contacting them directly to inquire. If it can be determined that those newer email messages after 2016 are available through the website, it means they're present on the server, and it would indicate an issue with the configuration of the Mail app.
If they're not visible on the website, it's not expected that they would download to your Mail app. In that case, we can recommend researching the steps to export mailboxes from Outlook to Mail. Contact Microsoft Support directly for instructions using Outlook to export, then you may refer to the guide we shared previously for the steps to import.
Regarding the issue with white text on a black background in Mail, it sounds like you've got Dark Mode enabled on your Mac. This feature can be set to turn on automatically at certain times, or disabled altogether. Here's a guide with detailed information to help configure Dark Mode in a way that works best for you:
How to use Dark Mode on your Mac
Have a great day!