SMTP (Simple Mail Transfer Protocol)
SMTP is the industry standard protocol for sending email. If you’re looking to send email, then you’ll use SMTP instead of IMAP. An SMTP relay service can help you send email without having to build your own SMTP server.
IMAP (Internet Access Message Protocol)
IMAP is one of the most common protocols for receiving email. IMAP syncs messages across all devices.
POP (Post Office Protocol)
POP3 is another protocol for receiving email on a single device. Using POP3 means that your email will be accessible offline and deleted from the server.