SMTP (Simple Mail Transfer Protocol): How It Works and Why It’s Necessary

SMTP (Simple Mail Transfer Protocol) is a common language used to send email. It’s a universal set of rules that allow servers and email clients to communicate via the internet.

Think of SMTP as the language your computer uses to tell a server where an email goes, what’s in the email, what’s attached, and more. It’s similar to putting the address and subject on an envelope to help the mailman deliver your letter.

While SMTP is used to send emails, IMAP is the standard protocol for retrieving emails. Most servers and email clients use these protocols in conjunction to distribute mail flow.

SMTP started in 1980 and was widely used by the early 80s. It commonly uses port 25 to relay messages between servers and port 587 for submissions between mail clients to mail servers.

An SMTP server is an application that connects to an email client (through port 25 or 587, usually) to deliver emails. When you send an email, the email client converts the message into code that specifies the sender’s address, receiver’s address, and the contents of the email.

It then transfers the code to the SMTP server, where the server processes the code and relays it to the corresponding email address. The SMTP server verifies the sender’s IP addresses to prevent spam. Servers can also use authentication protocols like DKIM, SPF, and DMARC to ensure emails are not malicious.

If the email addresses are accurate and the IP address is active and verified, your email is delivered. Delivery servers usually reject IP addresses that aren’t validated to a trusted domain, so SMTP is necessary to prevent spam designation.

SMTP uses DNS to convert domain names into associated servers and IP addresses.

SMTP servers have specific addresses to communicate with other servers and mail clients. Most server addresses are formatted as smtp.exampledomain.com or smtp.mail.exampledomain.com. Here are a few common examples:

• Gmail: smtp.gmail.com

• Yahoo: smtp.mail.yahoo.com

• Outlook: smtp-mail.outlook.com

SMTP server addresses are usually available in a mail client's settings or accounts sections. If you can’t find it, contact your administrator or ISP.

If you’d like to successfully send emails, SMTP is necessary, especially at an enterprise level with substantial mail flow. Your email server or client uses it to send messages to other servers. That’s not the only useful feature:

• SMTP helps prevent spam by verifying the sender’s account before delivering an email.

• By preventing spam emails, SMTP also protects your IP reputation.

• SMTP increases delivery rate by restricting spam and protecting IP reputation.

• SMTP notifies senders if an email address is invalid or incorrect.

• It’s a universal, trusted protocol that other servers and clients use.

In short, SMTP is an important part of sending and receiving emails. Without adhering to SMTP, you can easily find your email address on the blocklist from major email providers. It’s especially important for enterprises that send hundreds of emails a day–without an SMTP server, there’s a good chance those emails won’t be successfully delivered.

SMTP uses commands to communicate between servers while processing and delivering emails. These are some commonly used commands:

1. HELO: Identifies the email sender’s server and domain name

2. MAIL FROM: Specifies the sender’s email address

3. RCPT: Identifies the email’s recipient

4. DATA: This command signals the beginning of the email’s content

5. QUIT: Ends the SMTP server connection

You can set up and run your own SMTP server, or simply use a third-party server. What’s better?

For most users, a third-party server is an easy choice. It’s significantly easier, and it’s usually cheaper and safer. And there’s a good chance you’ll have better deliverability rates by using a third-party server.

If you create your own local SMTP server, you don’t have to worry about outgoing email limits, and you have more control over privacy. But you’ll likely have deliverability issues, and it will require time, effort, and money.