Introduction
Telnet can be used to manually test SMTP mail sending by communicating directly with a mail server. This method is commonly used for troubleshooting mail delivery issues and verifying SMTP server responses.
Prerequisites
Before using telnet for sending mail, ensure the following:
- Telnet client is installed on your system
- SMTP server is reachable on port 25
- You have a valid sender email address
- You know the recipient email address
- Firewall allows outbound connection to port 25
To install telnet (if not installed):
sudo apt install telnet # Ubuntu/Debian sudo yum install telnet # CentOS/RHEL
Steps to Send Mail via Telnet
Step 1: Connect to SMTP Server
Connect to your mail server on port 25:
telnet your-mail-server.com 25
You should see a response like:
220 mail.example.com ESMTP Postfix
Step 2: Identify Yourself (HELO/EHLO)
HELO your_domain.com
Response:
250 Hello
Step 3: Set Sender Email
MAIL FROM:<you@hostname.com>
Response:
250 OK
Step 4: Set Recipient Email
RCPT TO:<them@someplace.com>
Response:
250 OK
Step 5: Enter Message Body
DATA
Then type your email content:
Subject: Test Mail via Telnet Hello, This is a test email sent using telnet SMTP. Regards, Admin
End the message with a single dot (.) on a new line:
.
Response:
250 OK: queued as XXXXX
Step 6: Quit Session
QUIT
Response:
221 Bye
Conclusion
Sending mail via Telnet is a useful method to test SMTP connectivity and troubleshoot mail delivery issues. It helps verify whether the mail server is accepting connections and processing emails correctly at the protocol level.