SMTP

SMTP is a short for Simple Mail Transfer Protocol and it is used to transfer e-mail messages between computers. It is a text based protocol and in this, message text is specified along with the recipients of the message. Simple Mail Transfer Protocol is a 'push' protocol and it cannot be used to 'pull' the messages from the server.

The ability to provide E-mail services to clients includes two critical functions: SMTP and POP3. Together, they provide the means for clients to send outgoing mail and check for new incoming mail, respectively.

SMTP is used to send the message from the mail client to the mail server and an e-mail client using the POP or IMAP is used to retrieve the message from the server.

An SMTP server performs the following two functions :

1. It verifies the configuration and grants the permission to a computer that is making an attempt to send a message. It sends the message to the specified destination and tracks it to see whether it's delivered successfully or not. If it's not delivered successfully then an error message is send to the sender.

2. There's one limitation to SMTP and it's the inability to authenticate the senders and this results in e-mail spamming. The enhanced version of SMTP also exists and it?s called as Extended SMTP (ESMTP). ESMTP is used to send the e-mails that include graphics and other attachments.

What is SMTP Relay?

SMTP Relay is a service provided by most modern SMTP Servers. Whenever you send email to someone that is not on the same network as you are, somebody will need to deliver that email. This includes retrying in case the connection on the other party is slow and, in some cases, sending bounce back messages, informing you that this recepient cannot be reached. If you utilize an ISP's server, you can most likely count on the fact, that the server will be always up and running for you when you need it.