Testing SMTP Configuration with Python

Introduction

Have you ever found yourself in a situation where you need to configure SMTP for an application, but you're not quite sure if the credentials you have are correct? Or maybe you're debugging an issue where emails aren't being sent, and you want to rule out credential issues.

I recently faced a case where I was asked to test an SMTP configuration. I was a bit confused about how to verify it quickly without setting up a full-blown application. To solve this, I created a simple Python script to test the SMTP connection and send a test email. This ensures that the SMTP credentials are valid before integrating them into a larger system.

In this post, I'll share that script with you. You can also view the full source code here: https://github.com/billy93/Test-Email.

Prerequisites

To use this script, you'll need Python installed. We'll also use the python-dotenv library to manage environment variables securely.

First, install the required package:

pip install python-dotenv

The Python Script

Here is the main.py script. It loads the SMTP configuration from environment variables and attempts to send a simple email.

import os
import smtplib
from email.message import EmailMessage
from dotenv import load_dotenv

# Load env variables
load_dotenv()

MAIL_HOST = os.getenv("MAIL_HOST")
MAIL_PORT = int(os.getenv("MAIL_PORT"))
MAIL_USERNAME = os.getenv("MAIL_USERNAME")
MAIL_PASSWORD = os.getenv("MAIL_PASSWORD")
MAIL_FROM = os.getenv("MAIL_FROM")
MAIL_TO = os.getenv("MAIL_TO")

def send_email():
    msg = EmailMessage()
    msg["Subject"] = "Test Email from Python"
    msg["From"] = MAIL_FROM
    msg["To"] = MAIL_TO
    msg.set_content("Ini email test dikirim dari aplikasi Python 🚀")

    try:
        with smtplib.SMTP(MAIL_HOST, MAIL_PORT) as server:
            server.ehlo()
            server.starttls()  # starttls.enable = true
            server.ehlo()
            server.login(MAIL_USERNAME, MAIL_PASSWORD)  # smtp.auth = true
            server.send_message(msg)

        print("✅ Email berhasil dikirim")

    except Exception as e:
        print("❌ Gagal kirim email")
        print(e)

if __name__ == "__main__":
    send_email()

Configuration

Create a .env file in the same directory as your script with your SMTP details:

MAIL_HOST=smtp.example.com
MAIL_PORT=587
MAIL_USERNAME=your_username
MAIL_PASSWORD=your_password
MAIL_FROM=sender@example.com
MAIL_TO=recipient@example.com

How It Works

1. Environment Variables: The script uses dotenv to load sensitive information like passwords and hosts from the .env file, keeping them out of your code.
2. Email Construction: We use EmailMessage to construct a simple email with a subject, sender, recipient, and body content.
3. SMTP Connection:
   • It connects to the MAIL_HOST on the specified MAIL_PORT.
   • server.starttls() is called to upgrade the connection to a secure encrypted SSL/TLS connection.
   • server.login() authenticates the user.
   • server.send_message() sends the email.
4. Error Handling: The try-except block catches any exceptions (like authentication errors or connection timeouts) and prints a failure message.

Running the Test

Run the script using Python:

python main.py

If everything is configured correctly, you should see:

✅ Email berhasil dikirim

And the recipient should receive the test email. If there's an error, the script will output:

❌ Gagal kirim email
[Error details...]

Conclusion

This simple script has been a lifesaver for me when verifying SMTP credentials. It isolates the SMTP sending logic, allowing you to debug configuration issues without the noise of a larger application.

Happy coding!