What is SMTP?
SMTP (Simple Mail Transfer Protocol) is the standard protocol for sending emails across the internet, defining how email messages are transmitted between mail servers.
SMTP (Simple Mail Transfer Protocol) is the fundamental protocol that powers email delivery across the internet. When you send an email, your mail client or application connects to an SMTP server, which then routes the message through the internet to the recipient's mail server.
SMTP has been the backbone of email since 1982. It defines how email clients connect to servers, how servers communicate with each other, and how messages are formatted and transmitted. While the protocol is simple, modern implementations add security (TLS encryption), authentication, and extensions for features like delivery notifications.
For developers, SMTP relay is a common way to send transactional emails. Your application connects to an SMTP server (like Ark's) and sends emails using SMTP commands. The relay service then handles delivery, authentication, and retry logic.
Why SMTP Matters
SMTP is the universal language of email. Understanding it helps you debug delivery issues, configure email services, and choose between SMTP and API integration. While APIs are often easier, SMTP remains important for legacy systems, email clients, and situations requiring maximum compatibility.
Frequently Asked Questions
What's the difference between SMTP and IMAP?
SMTP is for sending email—it transmits messages from sender to recipient. IMAP (and POP3) are for receiving email—they let email clients retrieve messages from a mail server.
What port should I use for SMTP?
Port 587 with STARTTLS is the modern standard for authenticated email submission. Port 465 with implicit TLS is also widely supported. Avoid port 25 for email submission—it's meant for server-to-server communication and is often blocked.
Why do emails sent via SMTP sometimes fail?
Common issues include incorrect credentials, wrong port, missing TLS, authentication problems, or the receiving server rejecting the email due to spam filters or authentication failures (SPF/DKIM).
Is SMTP secure?
Modern SMTP uses TLS encryption to secure the connection. Always use STARTTLS (port 587) or implicit TLS (port 465). Never send credentials or emails over unencrypted connections.
Related Terms
Email API
An email API (Application Programming Interface) allows developers to send, receive, and manage emai...
Transactional Email
Transactional emails are automated messages triggered by user actions, such as password resets, orde...
DNS Records
DNS records for email are entries in your domain's DNS that configure mail delivery (MX), sender aut...
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