Put the news into letters!

When you deploy a program on a remote server debugging and monitoring your scripts gets harder since you will have to log in to the server in order to read logs. To make the monitoring easier you could implement a function that sends you a mail with some debugging information in case of an error.

In this exercise we are going to write our own really small and dead simple implementation of a mailing list or group notification system using Python. Our goal is to write a script that gathers some mail addresses from a predefined server and uses a text file as source for some kind of newsletter.

To get started, we are going to need some recipients. Since using leaked mail addresses found on darknet marketplaces is kind of illegal and might cause us some stress, let’s just use a list of “voluntary recipients” from our web server.

Gather Recipients

Let’s assume https://fsr.github.io/python-lessons/misc/recipients.json contains a well maintained list of mailing list subscribers that thirst for your mail.

Get the recipient list from the web server¹ and parse the addresses. As you can see from taking a look into the file, it’s a JSON. So let’s use the json module for the parsing.

Content

Before we can send anything, we need that anything. We need content. Write some content in a plain text file. This will be the text we will send to our recipients afterwards.
As we would be very pleased to get some feedback for this course, feel free to write some lines about how you liked this course! Otherwise, you can be creative and write what ever you want.

After you’ve written a small piece of text, read it from the file. Note that you can use f.read() here instead of f.readlines():

with open(filename) as f:
    content = f.read()

print(content)  # contains a single multiline string

Build the Mail!

Even though we haven’t configured the mail account yet, let’s build the mail object itself and prepare it for sending.

Initialize the MIMEText object with the content you already read from the file and add more information regarding sender and recipient(s) of the mail:

# initialize the message object

message['From'] = 'Your Name <mail@example.com>'
message['To'] = 'Poor Guy <alwaysgetsspammed@badluckbri.an>'
# you might set more inforamtion like the Subject and Cc/Bcc

Set the subject of your mail and use a timestamp within the subject to indicate when the mail has been sent.²

Verify it works

Set your own mail address as hidden CC (Bcc) to verify your program and the mail sending work as expected.

Adjust the settings

Now comes the part where we make a connection to the server and authenticate to send the mail we just built. Use the context manager to open a SMTP connection and log in with the user data we provide you with. Don’t forget to enable starttls before starting!

After the login was successful, you can use smtplib.send_message(...) to send your own mail to the world.

Know your Errors

Don’t forget the error handling! Try to catch every error that could occur to make your script run as safe as possible!