HowTo: Send Email from an SMTP Server using the Command Line

The SMTP (Simple Mail Transfer Protocol) is an Internet standard for electronic mail (Email) transmission across Internet Protocol (IP) networks.

This tutorial shows how to connect to SMTP mail server and send an Email using the ‘telnet’ command.

Step 1: Open a connection from your computer to an SMTP mail server

$ telnet smtp.domain.ext 25
220 smtp.domain.ext ESMTP Sendmail ?version-number?; ?date+time+gmtoffset?

• smtp.domain.ext – Your mail server;
• 25 – Default port for SMTP.

Step 2: Declare your domain name or IP-address

You can set local.domain.name or anything you want in ‘HELO’, because the server doesn’t check its authenticity, that is one of the drawbacks of this protocol.

> HELO local.domain.name
250 smtp.domain.ext Hello local.domain.name [xxx.xxx.xxx.xxx], pleased to meet you

Step 3: Set sender’s email

> MAIL FROM: sender@adress.ext
250 2.1.0 sender@adress.ext... Sender ok

Step 4: Set recipient’s email

> RCPT TO: recipient@adress.ext
250 2.1.5 recipient@adress.ext... Recipient ok

Step 5: To write the message, type DATA and press ‘Enter’

> DATA
354 Enter mail, end with "." on a line by itself

Step 6: On the first line type ‘SUBJECT: Your Subject’ and press ‘Enter’ twice

> SUBJECT: Test message

Step 7: Continue typing your message

Hello,
this is a TEST message, 
please don't reply.
Thank you.

Step 8: Put a single period (.) on a line by itself and press ‘Enter’ to send your message.

> .
250 2.0.0 ???????? Message accepted for delivery

Step 9: Close the connection

> QUIT
221 2.0.0 server.com closing connection