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What is SMTP and how does it allow email sending?

SMTP (Simple Mail Transfer Protocol): what it is, what it's for, and how it relates to email within a hosting service.

Glossary

Quick summary

  • What it is: SMTP (Simple Mail Transfer Protocol) is the standard protocol used on the Internet for transmitting email messages between systems.
  • What it's for: it helps configure, send, receive and protect email for a domain.
  • When to check it: when creating email accounts, configuring an email client or investigating sending and receiving issues.

SMTP (Simple Mail Transfer Protocol) is the standard protocol used on the Internet for transmitting email messages between systems. It is responsible for sending messages from one mail server to another. SMTP only handles message sending, not reception or storage.

Main features of SMTP

  • Sending only: SMTP is used exclusively for sending messages. To receive emails, protocols such as POP3 or IMAP are used.
  • Network ports: Operates through port 25 for unencrypted connections, and ports 587 or 465 for connections encrypted with SSL/TLS.
  • Simple and efficient: Designed to transfer messages quickly between mail servers.

How SMTP works

  1. Connection: The email client connects to an SMTP server and sends the message along with routing instructions (recipient's address).
  2. Routing: The SMTP server determines where to send the message by querying the DNS to find the destination domain's receiving mail server.
  3. Transfer: The SMTP server transfers the message to the receiving server, potentially involving several intermediate hops.
  4. Final delivery: Once the email arrives at the recipient's server, the SMTP process concludes. From there, POP3 or IMAP handle storing and delivering the message to the user.

Security in SMTP

  • Authentication: SMTP supports authentication extensions that prevent system abuse and spam sending.
  • TLS encryption: The use of TLS encrypts the SMTP connection and protects data during transmission.
  • SPF and DKIM: Additional technologies that validate messages and verify that the sending server is authorized by the sender's domain.

When will you encounter it?

The term SMTP appears when configuring an email client (Outlook, Thunderbird), when configuring email sending options in the hosting control panel, or in server logs when investigating email delivery issues.

Why it matters in hosting

Understanding this concept will help you make better decisions when managing your service. In practice, it relates to configuring, delivering, receiving and protecting email for a domain. If it appears in a guide, the control panel or a support response, review the context before making changes.

Related articles

  • Webmail
  • IMAP
  • POP3
  • SPF
  • DKIM