I sent an email via protonmail. I then closed my account. Can you trace my email from this?
Can you trace my email from this?
This is a very bad way of formulating your question, as it does not define what threat you are trying to defend yourself against.
Scenario 1 - The Sandwich Case
I got angry at my co-worker for stealing my sandwich and wrote an angry e-mail at him. Can he or the company figure out it was me?
Perhaps, but probably not by technical means. They would ask your co-worker why anyone would write a message like this to him, he'd admit he ate your sandwich and the rest is putting two and two together.
Scenario 2 - The Angry Ex
My girlfriend recently left me and I wrote an angry e-mail at her. I may have threatened her somewhat, but I didn't mean it. Can she go to the police? Can the police figure out it was me?
Similar to the above scenario, it's probably clear it was you, just by it being obvious. Can it be proven? That's a different question, but it's possible.
Scenario 3 - Help I didn't study for the finals so I sent a bomb threat
I didn't study for the finals, panicked and sent an anonymous bomb threat to my university. Don't judge me, it seemed like a good idea at the time! How screwed am I?
Very. Depending on how serious the university and local authorities take this (usually very seriously), it could be treated as a terrorist threat and providers like Protonmail usually cooperate with authorities in such cases.
So my advice for you is, don't send anonymous bomb threats - or any bomb threats for that matter - and study for your finals next time.