Editing Simple Mail Transfer Protocol (section)

{{Short description|Internet protocol used for relaying e-mails}}
{{Distinguish|SMTP, Inc.|GSM 03.40{{!}}Short Message Transfer Protocol}}
{{Use mdy dates|date=October 2013}}
{{Infobox networking protocol
| title        = Simple Mail Transfer Protocol
| logo         = 
| logo alt     = 
| image        = 
| image alt    = 
| caption      = 
| is stack     = 
| abbreviation = SMTP
| purpose      = Electronic mail transmission protocol
| developer    = 
| date         = {{Start date and age|1981|11|  }}
| based on     = 
| influenced   = 
| osilayer     = [[Application layer]]
| ports        = 465, 587, 25 
| rfcs         = RFC 5321
| hardware     = 
}}
{{IPstack}}
The '''Simple Mail Transfer Protocol''' ('''SMTP''') is an [[Internet Standard|Internet standard]] [[communication protocol]] for [[email|electronic mail]] transmission. Mail servers and other [[message transfer agent]]s use SMTP to send and receive mail messages. User-level [[email client]]s typically use SMTP only for sending messages to a mail server for relaying, and typically submit outgoing email to the mail server on port 465 or 587 per {{IETF RFC|8314}}. For retrieving messages, [[Internet Message Access Protocol|IMAP]] (which replaced the older [[Post Office Protocol|POP3]]) is standard, but proprietary servers also often implement proprietary protocols, e.g., [[Exchange ActiveSync]].

SMTP's origins began in 1980, building on concepts implemented on the [[ARPANET]] since 1971. It has been updated, modified and extended multiple times. The protocol version in common use today has extensible structure with various extensions for [[SMTP Authentication|authentication]], [[Email encryption|encryption]], binary data transfer, and [[International email|internationalized email addresses]]. SMTP servers commonly use the [[Transmission Control Protocol]] on [[port number]] 25 (between servers) and 587 (for submission from authenticated clients), both with or without encryption, and 465 with encryption for submission.