How do I implement the backend part for mail on JS, give me a hint

I have a creative task to create an analog of mail. I understand the frontend, but I have no idea about the backend at all =(. Don’t hit me =). I need to figure out how to make a server for this application. We are given a json database file with the project source data. “All application statics should be distributed by the server.”
To implement the API, it is forbidden to use any libraries on the backend, except for the standard ones for Node.js version 18.12.1 (LTS).
I would like to hear from those people who understand this, which way I should move to do this. Then I’ll figure it out myself. Thanks!!!
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