For new knowledge explain your understanding of how something works to a chatBot. Exlaining it will organize your thoughts and help you find holes in your understanding and AI’s are pretty good pointing out corrections. Also much cheaper than a tutor. The reason this is mainly good for fundamentals rather then advanced knowledge is because fundamentals tend to be widely available and well documented so chatBots have more to train on.
If you find yourself doing something that your not comfortable with because you suspect you lack expertise then start creating a reference document for yourself.
#routing and #security then and then subheadings for lower level concepts like ##DKIM, ##SPF under the security heading and ##MX Records in the routing heading. Then even further down explain things like syntax composition of things like SPF records: ###SPF Record Composition.