SMTP: What Is It?

SMTP, short for Simple Mail Transfer Protocol, is the core protocol for sending email over the Internet, from the sender to the SMTP server and between email servers. Though perhaps not as simple as its name suggests, this robust text-based protocol is the primary transmission medium of Internet mail and forms the backbone of the Internet's messaging system, taking care of transferring mail from user to user across TCP/IP networks. Indeed, SMTP happens to be the key component of the TCP/IP electronic mail system, and the sole part of the system that does not utilize SMTP for the final retrieval of the delivered email by recipient (this is performed by a retrieval protocol).

Email servers and mail transfer agents (MTA) utilize SMTP to both send and receive mail. But as the message completes the route from the initial outgoing email server to the destination server, it is retrieved by the recipient's email client via one of the standard mail retrieval protocols (POP or IMAP) that are complementary to SMTP (which handles only outgoing and not incoming email).

Additionally, SMTP is employed to submit email from an email client application to an email server for further relaying. For this reason, both the outgoing (SMTP) server and the incoming (POP or IMAP) server generally need to be specified in the configuration of an email application. Emails clients (a particular kind of user agent) are normally configured to submit all email to a single MTA, specified in the configuration parameter "outgoing mail server."Under SMTP, the mail sender "talks" to the mail receiver via SMTP commands (there are over a dozen of them, each of which contains four letters) and transfers requisite data over the Transmission Control Protocol (TCP) layer. SMTP relay begins by specifying the sender, then the recipient(s) of an email message, and once their existence has been verified, the message body itself is transferred. (The availability of an SMTP connection may be tested easily by telnetting to port 25 of a remote SMTP server.)

How Does SMTP Relay Work?

Here is the SMTP delivery process in a nutshell. Once a message is composed, it needs to be submitted to outgoing email relay to begin its transfer across the Internet. The "Send" button is pressed, and the user-level mail client uses the Simple Mail Transfer Protocol to "talk" to the SMTP server, usually on the default TCP Port 25. The outgoing email server receives the message, saves it locally and queues it to be relayed along with other emails received. Since a direct connection between the users is not always possible, the path may be broken up into hops. The SMTP server looks up the destination domain's Mail Exchange (MX) record in the Domain Name System (DNS), and relays the message to a server listed in the record, again via port 25 and SMTP. Each successive SMTP session delivers the electronic message one hop further along the path toward the recipient. The process repeats itself at each hop until the message reaches the destination post office, assuming the delivery succeeded and no "fatal errors" occurred along the path.

OUTGOING SMTP SERVICE

We provide Outgoing Email Relay service for email marketing solutions. All SMTP accounts are provided in the format below:

Host: mail.domain.com

Username: xxxxxxxxxxxxxxxx

Password: xxxxxxxxxxxxxxxx

PRICING: $49.00 (Max 10,000 relays/month)