admin answers:

I just got this from the Google website.

What’s the difference between IMAP and POP?
Unlike POP, IMAP offers two-way communication between your web Gmail and your email client(s). This means when you log in to Gmail using a web browser, actions you perform on email clients and mobile devices (ex: putting mail in a ‘work’ folder) will instantly and automatically appear in Gmail (ex: it will already have a ‘work’ label on that email the next time you sign in).

IMAP also provides a better method to access your mail from multiple devices. If you check your email at work, on your mobile phone, and again at home, IMAP ensures that new mail is accessible from any device at any given time.

Finally, IMAP offers a more stable experience overall. Whereas POP is prone to losing messages or downloading the same messages multiple times, IMAP avoids this through two-way syncing capabilities between your mail clients and your web Gmail.

If you’re trying to decide between using POP and using IMAP with Gmail, we recommend IMAP.