VBR information can be used by a message transfer agent, a mail delivery agent or by an email client.

Clients were in effect Message Transfer Agents (MTAs) for their own postoffices.

Message transfer agent (MTA)

The primary disadvantage of many message oriented middleware systems is that they require an extra component in the architecture, the message transfer agent (message broker).

MMDF, the Multichannel Memorandum Distribution Facility, is a message transfer agent (MTA), a computer program designed to transmit email.

Within the Internet mail architecture, local message delivery is achieved through a process of handling messages from the message transfer agent, and storing mail into the recipient's environment (typically a mailbox).

Many Mail Handling Software products bundle multiple message delivery agents with the message transfer agent component, providing for site customization of the specifics of mail delivery to a user.

A smart host is a type of email message transfer agent which allows an SMTP server to route email to an intermediate mailserver rather than directly to the recipient's server.

A message transfer agent receives mail from either another MTA, a mail submission agent (MSA), or a mail user agent (MUA).

If the server rejects the sender, the unauthorized client should receive a rejection message, and if that client was a relaying message transfer agent (MTA), a bounce message to the original sending address may be generated.

Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client-server application architecture.

The DNS server for the domain, , responds with any MX records listing the mail exchange servers for that domain, in this case , a message transfer agent (MTA) server run by Bob's ISP.

DSN refers to both a service that may optionally be provided by Message Transfer Agents (MTAs) using the Simple Mail Transfer Protocol (SMTP), and a message format to be used to return indications of message delivery to the sender of that message.