What is SMTP?

Have you ever wondered what SMTP is? No? Don’t worry. This post will explain to you what SMTP is, how it works and how you can configure it. Are you ready? Off we go.

What is SMTP?

SMTP (Simple Mail Transfer Protocol) is a simple protocol for email transfer that is used to exchange emails between mail servers via email programmes (an SMTP server is called Outgoing Mail Server).

How does SMTP work?

SMTP is a standard protocol for sending emails online. Its operation is quite simple and can be performed in five steps. An e‑mail can be sent via any email client, e.g. Outlook, Thunderbird, Roundcube or Gmail. Obviously, you can send your messages both via an email programme installed on your machine and browser email clients.

SMTP works by initializing the mail service to establish a two-way connection between the SMTP server sending the message and SMTP receiving this email. The SMTP sending server sends the comments the receiving server answers. After the transmission channel has been established with relevant comments, the sending server sends MAIL command, which indicates the message to be sent.

If the receiving server receives the message, it sends OK command. When the sending receives it, it sends RCPT command, which identifies the recipient. If the indication is correct, the receiving SMTP server sends an answer using OK command.

If you wish to send messages by using SMTP mail server, the receiving server must obtain information about the name of the sender’s server along with its name of the mailbox. In order to do that, MAIL command might include a return path, which specifies the sender’s address.

Apart from the MAIL process, which allows you to use MAIL, RCPT commends and the DATA command (a message to be sent commands, SMTP also allow you to perform redirection processes and verification and expansion of your recipient list.

SMTP – setting up an email programme

Setting up an SMTP server is quite simple. You just have to go to the basic settings of the email programme you use, where you have to find email settings. Next, you should configure a function for emails sent by your email programme.

When setting up an SMTP server in the mail programme, you should enter the SMTP server address, your email address, username, and port, and check the optional encryption of the connection established during the mail communication.

Below you can find example gmail.com account used during SMTP server configuration:

• SMTP server address – smtp.gmail.com
• Email address – twójemail@gmail.com
• User – twójemail@gmail.com
• Password – twojehaslo
• Port – 587
• Connection encryption – TLS.

What are the limitations of SMTP?

SMTP has one serious limitation: it makes it impossible to verify the sender of an e‑mail. This means the configuration and settings of the SMTP server don’t provide effective protection against spam and phishing attacks.

SMTP-AUTH extension provides a solution to this problem. It partially forces the sender to use an authorization mechanism when the emails are multiplied. Unfortunately, there is still no effective communication protocol for emails transmission online that would allow you to verify and authenticate the sender of the message.

Take a look at these articles as well:

• What is hosting?
• How to create your own email?
• Compendium: What should you know about the Internet domain?