http://protonmailrmez3lotccipshtkleegetolb73fuirgj7r4o4vfu7ozyd.onion/blog/smtp-imap-pop3
(new window) POP3 supports various secure authentication methods, and its simplicity is sometimes seen as one of its key strengths. There is very little that can go wrong. The downside of this simplicity is that POP3 offers no advanced email management functions.