I want to add a new email account to my "mail" client, but I don't want to download all of my "old" emails from the server (there are thousands). I just want to start with today's going forward. Is this possible?
Before downloading from the server, archive the mail you don't want to see. Do a search for instructions of how to do this for your client: "archive apple mail", "archive gmail", "archive thunderbird", etc.