New M1 Mac Mini hard drive full of emails (over 350gb of emails)

I just got a new M1 mac Mini at my job, and just as I am getting used to the more streamlined machine, my hard drive says its completely full. I go check out the hard drive allocation and see that my entire hard drive is being overrun by my email account. I should not have 400 gb of emails, by the way. I think it might just be the fact that we migrated an old state of my computer to this new one and the old mail app glitched out, possibly... Maybe it's a compatibility issue with Big Sur. I do not know, but I do hope someone can help me answer this question, because my hard drive should be nice and fresh and empty right now.