Comment by matrss

If I instruct fastmail or another provider to fetch mail from a different email provider on my behalf so that I have it in one place then that is a deliberate decision I make. If I connect to my mail provider via IMAP/SMTP from a local application (Outlook, Thunderbird, mutt or whatever) I do not expect my credentials to be exfiltrated to a third party so that they can also fetch my mail. In fact, I would consider that to be criminal behavior if not VERY clearly communicated, with all it's implications.