Once upon a time a (fameous) CS professor reported that his email was annoyingly slow. He was using the good ol' mailx MUA. He never deleted emails. He never

Once upon a time a (fameous) CS professor reported that his email was annoyingly slow. He was using the good ol' mailx MUA. He never deleted emails. He never moved emails out of his inbox. He had been doing this for many years. His .mbox file was many, many megabytes. Apparently, he had never noticed the problem before because he very rarely logged out, but IIRC some system work meant he needed to do so several times just prior to his complaint.