As a seasoned Python developer, I am planning to start a new blog series where I will be covering different Python command-line modules which come pre-installed with your Python installation. In this blog, we will be looking into the Python smtpd module, which allows you to run your own local SMTP server for email testing.

The smtpd module, short for Simple Mail Transfer Protocol Daemon, allows developers to set up and run their own local SMTP server. This functionality is particularly useful for testing email-related features during development. Rather than relying on external email servers, developers can take advantage of smtpd to simulate email transactions in a local environment.

It’s part of Python’s standard library, making it readily available for use in any Python project without the need for installing additional dependencies. At its core, this module provides a simple and lightweight implementation of an SMTP (Simple Mail Transfer Protocol) server. SMTP is the protocol used for transmitting electronic mail over the internet, and the smtpd module allows developers to create their own custom SMTP servers.

Setting up smtpd server.

In order to run smtpd server locally you need to perform the following steps,

  1. Open a Terminal and run the following command
python -m smtpd -n -c DebuggingServer localhost:1025

Breakdown of the command options:

  • -n: Prevents the server from attempting to verify the existence of the sender’s email address. (since we are testing with random email addresses).
  • -c DebuggingServer: Specifies the class to be used for the SMTP server, in this case, DebuggingServer as we are testing email functionality.
  • localhost:1025 : Sets the address and port on which the server will listen. You can choose a different port if needed.

Now this command while run our smtp server locally which we can use to test emails.

Writing a simple python script.

Once we have smtpd running, we can write a simple script to test it.

After creating that script you can simply run it. Once you run it you should see the following output on terminal where your smtpd command is running.

---------- MESSAGE FOLLOWS ----------
b'Content-Type: text/plain; charset="us-ascii"'
b'MIME-Version: 1.0'
b'Content-Transfer-Encoding: 7bit'
b'Subject: Test Email'
b'From: testing_email@xyz.com'
b'To: recipient_test@abc.com'
b'X-Peer: ::1'
b''
b'This is a test email'
b' Hello World'
------------ END MESSAGE ------------

Conclusion

Python is an awesome language, and it comes with lots of powerful command-line modules preinstalled. I hope you had a chance to learn something new! In future blog posts I will be covering more of these preinstalled command-line modules. If you have any feedback, please feel free to leave a comment below. If you prefer not to comment publicly, you can always send me an email.

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