Student continues to email me after I told him I would not regrade his paper. Do I need to reply? I have a student who wrote a final paper for a class in a masters program. He was disappointed with his grade. His paper had extensive copying, so I had a zoom call with him explaining why that was a problem, and then both my teaching assistant and I gave extensive written feedback on his paper, final grade of 69. He has written several times about it, claming that we took points off unfairly. I re-explained why points were taken off, and where, He writes back "but I thought the grading rubric meant..." or "I explained this, here is what I meant", etc. After five go arounds, I said I had nothing further to say, so I would no longer reply, and he would need to raise this with the department if he would like further review. Today, he sent me an extensive email again re-hashing points that I have clarified and explained again. I should add that he has a history of grade grubbing. Since I told him in 2 emails that the mattter was closed, and I would no longer reply, do I need to reply? Thank you.
No, you don't need to reply, but you should make sure that you retain all evidence for your decisions in the event the student complains to some higher authority. Retain the email thread as well. 

You've already said it was closed. Stick with that unless your chair or other such people force it to be reexamined.