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Email is submitted by a mail client (mail user agent, MUA) to a mail server (mail submission agent, MSA) using SMTP on TCP port 587. Most mailbox providers still allow submission on traditional port 25. The MSA delivers the mail to its mail transfer agent (MTA). Often, these two agents are instances of the same software launched with different ...
This is a list of TCP and UDP port numbers used by protocols for operation of network applications. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) only need one port for bidirectional traffic. TCP usually uses port numbers that match the services of the corresponding UDP implementations, if they exist, and vice versa.
To combat spam (including spam being sent unwittingly by a victim of a botnet) many ISPs and institutional networks restrict the ability to connect to remote MTAs on port 25. The accessibility of an MSA on port 587 [ 3 ] enables nomadic users (for example, those working on a laptop) to continue to send mail via their preferred submission ...
It can use a Transmission Control Protocol (TCP) transport like SMTP, but must not use port number 25, the well-known port for SMTP. Usage of port 24 ("any private mail system") is common among some mail server applications however. [2]
This is a list of Simple Mail Transfer Protocol (SMTP) response status codes. Status codes are issued by a server in response to a client's request made to the server. Unless otherwise stated, all status codes described here is part of the current SMTP standard, RFC 5321. The message phrases shown are typical, but any human-readable alternative ...
Late 1998 this was revoked when STARTTLS was standardized. [2] With STARTTLS, the same port can be used with or without TLS. The use of well-known ports for mail exchanges communicating with SMTP was discussed in particular at the time. [3] Port 465 currently shows [4] as registered for both Source-Specific Multicast [5] and submissions.
This article lists protocols, categorized by the nearest layer in the Open Systems Interconnection model.This list is not exclusive to only the OSI protocol family.Many of these protocols are originally based on the Internet Protocol Suite (TCP/IP) and other models and they often do not fit neatly into OSI layers.
Within the Internet email system, a message transfer agent (MTA), [1] mail transfer agent, [2] or mail relay is software that transfers electronic mail messages from one computer to another using the Simple Mail Transfer Protocol. [3] In some contexts, the alternative names mail server, mail exchanger, or MX host are used to describe an MTA.