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==Operation== ==Operation==
A message transfer agent receives mail from either another MTA, a ] (MSA), or a ] (MUA). The transmission details are specified by the ] (SMTP). When a recipient mailbox of a message is not hosted locally, the message is relayed, that is, forwarded to another MTA. Every time an MTA receives an email message, it adds a {{mono|Received}} trace header field to the top of the header of the message,<ref>See ] for the format of an email message. Many MUAs allow users to see the raw ''message source'' directly, thereby allowing header inspection.</ref> thereby building a sequential record of MTAs handling the message. The process of choosing a target MTA for the next hop is also described in SMTP, but can usually be overridden by configuring the MTA software with specific routes. A message transfer agent receives mail from either another MTA, a ] (MSA), or a ] (MUA). The transmission details are specified by the ] (SMTP). When a recipient mailbox of a message is not hosted locally, the message is relayed, that is, forwarded to another MTA. Every time an MTA receives an email message, it adds a {{mono|Received}} trace header field to the top of the header of the message,<ref>See ] for the format of an email message. Many MUAs allow users to see the raw ''message source'' directly, thereby allowing header inspection.</ref> thereby building a sequential record of MTAs handling the message. The process of choosing a target MTA for the next hop is also described in SMTP, but can usually be overridden by configuring the MTA software with specific routes.
⚫ An MTA works in the background, while the user usually interacts directly with a mail user agent. One may distinguish initial submission as first passing through an MSA—port 465 (or, for legacy reasons, optionally port 587) is used for communication between an MUA and an MSA, while port 25 is used for communication between MTAs, or from an MSA to an MTA.<ref>See table at this distinction is clarified in books,

]

⚫ An MTA works in the background, while the user usually interacts directly with a mail user agent. One may distinguish initial submission as first passing through an MSA—port 465 (or, for legacy reasons, optionally port 587) is used for communication between an MUA and an MSA, while port 25 is used for communication between MTAs, or from an MSA to an MTA.<ref>See table at ]</ref> this distinction is clarified in {{IETF RFC| 8314}}.


For recipients hosted locally, the final delivery of email to a recipient mailbox is the task of a ] (MDA). For this purpose the MTA transfers the message to the message handling service component of the message delivery agent (MDA). Upon final delivery, the {{mono|Return-Path}} field is added to the envelope to record the ]. For recipients hosted locally, the final delivery of email to a recipient mailbox is the task of a ] (MDA). For this purpose the MTA transfers the message to the message handling service component of the message delivery agent (MDA). Upon final delivery, the {{mono|Return-Path}} field is added to the envelope to record the ].

Revision as of 00:45, 23 December 2024

Software to transfer electronic mail

Within the Internet email system, a message transfer agent (MTA), mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using the Simple Mail Transfer Protocol. In some contexts, the alternative names mail server, mail exchanger, or MX host are used to describe an MTA.

Messages exchanged across networks are passed between mail servers, including any attached data files (such as images, multimedia, or documents). These servers often keep mailboxes for email. Access to this email by end users is typically either by webmail or an email client.

Operation

A message transfer agent receives mail from either another MTA, a mail submission agent (MSA), or a mail user agent (MUA). The transmission details are specified by the Simple Mail Transfer Protocol (SMTP). When a recipient mailbox of a message is not hosted locally, the message is relayed, that is, forwarded to another MTA. Every time an MTA receives an email message, it adds a Received trace header field to the top of the header of the message, thereby building a sequential record of MTAs handling the message. The process of choosing a target MTA for the next hop is also described in SMTP, but can usually be overridden by configuring the MTA software with specific routes. An MTA works in the background, while the user usually interacts directly with a mail user agent. One may distinguish initial submission as first passing through an MSA—port 465 (or, for legacy reasons, optionally port 587) is used for communication between an MUA and an MSA, while port 25 is used for communication between MTAs, or from an MSA to an MTA.Cite error: A <ref> tag is missing the closing </ref> (see the help page).

See also

References

  1. MTA=Message Transfer Agent (similar to X.400 name) is found, e.g., in RFC 1506, RFC 2476, RFC 3461, RFC 3464, RFC 3865, RFC 3888, RFC 6409, RFC 5598.
  2. MTA=Mail Transfer Agent (similar to Mail Transfer Protocol) is found, e.g., in RFC 2298, RFC 2305, RFC 3804, RFC 3798, RFC 4496, RFC 5442, RFC 5429.
  3. RFC 5598, Internet Mail Architecture, D. Crocker (July 2009).
  4. See Email#Message header for the format of an email message. Many MUAs allow users to see the raw message source directly, thereby allowing header inspection.
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