Quick Summary
SMTP (Simple Mail Transfer Protocol) is the standard internet protocol used for sending emails.
SMTP (Simple Mail Transfer Protocol) is the foundational protocol for email transmission. Defined in RFC 821 in 1982, it remains the backbone of all email systems today.
How SMTP Works
SMTP is built on a client-server model. When an email is sent, the email client (Outlook, Thunderbird, etc.) connects to an SMTP server. The server then relays the message to the recipient's email server.
The standard SMTP port is 25. For encrypted connections, port 587 (STARTTLS) and 465 (SSL/TLS) are commonly used.
SMTP Commands
EHLO/HELO: Initiates the connection.
MAIL FROM: Specifies the sender address.
RCPT TO: Specifies the recipient address.
DATA: Sends the message content.
QUIT: Closes the connection.
ONS Mail and SMTP
ONS Mail fully supports the SMTP protocol. It uses TLS encryption for secure SMTP connections and automatically configures authentication mechanisms.