What is Simple Mail Transfer Protocol ( SMTP ) ?, SMTP mail server?, SMTP protocol?, SMTP protocol used for?, SMTP Example
Simple Mail Transfer Protocol (SMTP)
Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (email) transmission. First defined by RFC 821 in 1982, it was last updated in 2008 with Extended SMTP additions by RFC 5321, which is the protocol in widespread use today.simple mail transfer protocol standard port 587
Although electronic mail servers and other mail transfer agents use SMTP to send and receive email messages, user-level client mail applications typically use SMTP only for sending messages to a mail server for relaying. For retrieving messages, client applications usually use either IMAP or POP3.
SMTP communication between mail servers uses TCP port 25. Mail clients on the other hand, often submit the outgoing emails to a mail server on port 587. Despite being deprecated, email providers sometimes still permit the use of nonstandard port 465 for this purpose.
SMTP connections secured by TLS, known as SMTPS, can be made using STARTTLS.
Although proprietary systems (such as Microsoft Exchange and IBM Notes) and webmail systems (such as Outlook.com, Gmail, and Yahoo! Mail) use their own non-standard protocols to access mailbox accounts on their own email servers, all use SMTP when sending or receiving an email from outside their own systems.
SMTP Protocol overview
SMTP is a connection-oriented, text-based protocol in which a mail sender communicates with a mail receiver by issuing command strings and supplying necessary data over a reliable ordered data stream channel, typically a Transmission Control Protocol (TCP) connection. An SMTP session consists of commands originated by an SMTP client (the initiating agent, sender, or transmitter) and corresponding responses from the SMTP server (the listening agent, or receiver) so that the session is opened, and session parameters are exchanged.
SMTP Spoofing and spamming
The original design of SMTP had no facility to authenticate senders, or check that servers were authorized to send on their behalf, with the result that email spoofing is possible, and commonly used in email spam and phishing.
Occasional proposals are made to modify SMTP extensively or replace it completely. One example of this is Internet Mail 2000, but neither it nor any other has made much headway in the face of the network effect of the huge installed base of classic SMTP. Instead, email servers now use a range of techniques, including DomainKeys, DomainKeys Identified Mail, Sender Policy Framework and DMARC, DNSBLs and greylisting to reject or quarantine suspicious emails.
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