Support Start > Email > Advanced Email Questions > IMAP > POP3 Connection Redownloads Old Mail

One of the potential problems of using a POP3 connection instead of an IMAP connection to read your mail is that with POP3, the computer or device on your end is what keeps track of which messages have previously been seen. The mail server on our end doesn’t track that.

If your computer or device loses track of what it's already seen due to a software bug, or if you get a new computer or device, it will have no way of knowing what it's already seen, and will re-download all the old mail as if each were a new message. There’s nothing we can do to help with that, since our server doesn’t control it.

Using IMAP instead of POP3 will avoid this problem, because with IMAP, the server (not your program or device) keeps track of what messages are new.