POP
Port 110 or 995 (SSL/TLS)
POP (Post Office Protocol) simply downloads email to your computer and then deletes the email from the server. If you access your email on more than one device (desktop, laptop, tablet or phone), your mailboxes will not synchronise.
IMAP
Port 143 or 993 (SSL/TLS)
IMAP (Internet Message Access Protocol) is the most modern and widely used protocol, which can download AND upload (synchronise) data with the server whereas the POP protocol is a download–only protocol and thus will not be able to upload data to a server. IMAP can synchronise advanced permissions and other folders and is also able to distinguish between already read/opened mail from device to device.