For this purpose the MTA transfers the message to the message handling service component of the message delivery agent (MDA). One may distinguish initial submission as first passing through an MSA-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 this distinction is first made in RFC 2476.įor recipients hosted locally, the final delivery of email to a recipient mailbox is the task of a message delivery agent (MDA).
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.Īn MTA works in the background, while the user usually interacts directly with a mail user agent. 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. When a recipient mailbox of a message is not hosted locally, the message is relayed, that is, forwarded to another MTA. The transmission details are specified by the Simple Mail Transfer Protocol (SMTP).
Access to this email by end users is typically either via webmail or an email client.Ī message transfer agent receives mail from either another MTA, a mail submission agent (MSA), or a mail user agent (MUA). These servers also often keep mailboxes for email. Messages exchanged across networks are passed between mail servers, including any attached data files (such as images, multimedia or documents). The terms mail server, mail exchanger, and MX host are also used in some contexts. Within the Internet email system, a message transfer agent ( MTA), or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using SMTP.
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