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 is one of the most common protocols for receiving email.
IMAP syncs messages across all devices.
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.