IMAP and POP3 are two ways an email application can retrieve messages from a mail server.
IMAP
IMAP keeps messages on the server and synchronizes mailbox folders between devices. It is usually the better choice when the same mailbox is used on a phone, computer, tablet, and Webmail.
POP3
POP3 is designed around downloading messages to a mail client. Depending on client behavior, downloaded messages can be removed from the server, which can make them unavailable from other devices.
Which should I choose?
For most modern multi-device use, choose IMAP. Choose POP3 only when you specifically want a download-oriented workflow and understand how your client handles server copies.
IMAP generally uses more server storage because mail remains on the server, so periodically review mailbox disk usage.
