What is SMTP?
The Simple Mail Transfer Protocol (SMTP) is a communication protocol used to transmit email between corresponding email servers. Using an email client like Mac Mail, Outlook, Thunderbird, or web clients like Gmail or Windows Live, SMTP can send messages to an email server. Although SMTP was initially designed as an email transport and delivery system, it later encompassed the email submission protocols that are now in use by both the Post Office Protocol (POP) and the Internet Message Access Protocol (IMAP). The above-noted email clients use these protocols to retrieve email from an email server. When this system fails, it provides the means to identify and resolve SMTP errors.