Amazon SDE-2 interview questions

In LLD round I was asked to design school management system. I listed down multiple services like course scheduling, events (exams, parent-teachers meet, co-curricular activities, accounts). After this the question was changed (we were already 20 min in the round). Interviewer asked me if I know how e-mail systems works (like Gmail), tbh I didn't and neither was I prepared for it, so I answered that I don't have much idea about it just know that they use SMTP protocol. Of course round went bad 'cause I wasn't prepared and I got rejected.