Simple Mail Transfer Protocol (SMTP) is an Internet standard for email transmission used by mail servers both to send and receive email, and by email client applications to send email to the mail server.
SMTP is the common language spoken throughout the email transmission world. Virtually ever mail server uses SMTP to send and receive email. When you use an email application such as Microsoft Outlook to send an email, the protocol used to send the email from the application to the mail server is SMTP. Proprietary email systems have also developed their own email transfer protocols for internal use, but when communicating outside of their own system all email systems use SMTP.
Frequently Asked Questions
Who developed SMTP? When was it first used?
The SMTP standard was first published in 1981 by the “god of the Internet”, Jon Postel. However, several electronic message transfer protocols released throughout the 1970s, including Mail Box Protocol, SNDMSG, FTP Mail, and Mail Protocol, provided the technical underpinnings on which SMTP was built.
SMTP was adopted rapidly and became the dominant electronic message transfer protocol in the 1980s, a position it still enjoys today.
What types of email programs use SMTP?
Virtually all email systems have proprietary communication protocols they employ when communicating with their own mail servers. However, once they step outside of their own system, they all use SMTP to send and receive email. Whether you use Microsoft Exchange, Gmail, Yahoo! Mail, or any other email service, SMTP is the protocol used when an email leaves your email provider's mail servers.
Are there any shortcoming inherent to SMTP?
While SMTP is used widely, it does have one inherent flaw that has been the cause of quite a bit of frustration. From its inception, SMTP has not provided any way to authenticate email senders. This allows knowledgeable spammers to mislead email recipients about who is sending them email by providing a false sender's address, a maneuver referred to as spoofing.
There have been several proposals to overhaul SMTP or replace it with a protocol that would eliminate this shortcoming. However, the massive installed base of SMTP means that every proposal made so far has faced an insurmountable level of resistance.
What's the difference between SMTP, POP3, and IMAP?
SMTP, POP3 or POP Server, and IMAP are the three protocols most commonly used to connect email clients to mail servers. However, they all serve different functions.
- SMTP: The protocol used to trasfer email from an email application to a mail server, and to send email from one mail server to another.
- POP3: Post Office Protocol (POP3) is a simple protocol used to allow an email client to download email messages from a mail server. When an email client is connected to a mail server by POP3 all email is downloaded at once, and the copies on the mail server are deleted.
- IMAP: Internet Message Access Propocol (IMAP) is similar to POP3, but offers additional features, such as the option to leave a copy of downloaded emails on the mail server.
In other words, POP3 and IMAP are basically download protocols used to transfer email from a mail server to an email application. SMTP is the message transfer protocol used to send email back to the mail server, and from one mail server to another over the Internet.