How to Send Automatic Recurring Emails in Python With SendGrid

February 06, 2023
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recurring emails in python

Businesses often need to send emails programmatically at specific times or regular intervals. You can set this up in Python using the Twilio SendGrid API with the Redis Queue and RQ Scheduler. Let's walk through how to automate email sending one step at a time.

What is the benefit of automated emails?

With automated emails, businesses can email customers based on event triggers or scheduling strategies. For example, in response to a webhook, a Python application can prepare an email and schedule it to send later.

Then, say a customer signs up for promotions by entering their email address in a web form. When they submit the form, this triggers a Python application that immediately sends a welcome email and schedules a follow-up email with a promotional discount for the next morning.

Sending emails programmatically with a service like SendGrid means you don’t risk forgetting about routine customer communication tasks. Gone are the days of time-consuming and error-prone manual emailing.

When you couple your Python application with SendGrid and take advantage of libraries like Redis Queue and RQ Scheduler, you’ll enter an email automation world with endless possibilities.

Prerequisites and dependencies for Python email automation

Before you start writing code, ensure you have the following:

  • The Python 3 software installed on your machine
  • A SendGrid account (the free tier is adequate for this demo)
  • An email address for testing out our email sending automation

With those pieces in place, install the following Python library dependencies:

  • sendgrid: You’ll need this to work with the SendGrid Web API.
  • rq-scheduler: You’ll need this lightweight, elegant solution built on top of the Redis Queue (rq), which we’ll use for simple task scheduling

Let’s walk through the following initial setup steps:

1. Create a virtual environment

First, create a virtual environment and activate it.

~$ python3 -m venv ./python-venvs
~$ source ./python-venvs/bin/activate
(python-venvs) ~$

Working within our virtual environment, we’ll create a project folder called demo.

(python-venvs) ~$ mkdir demo && cd demo
(python-venvs) ~/demo$ 

If you're working within a Windows environment, the commands to activate a virtual environment and create a demo directory would look like this:

c:\> c:\PATH\TO\PYTHON\python -m venv c:\PATH\TO\myenv
c:\> c:\PATH\TO\myenv\scripts\activate
c:\> mkdir c:\demo
c:\> cd c:\demo

2. Install the Python dependencies

Now, in our project folder, we can install the Python dependencies we’ll need:

(python-venvs) ~/demo$ pip install sendgrid rq-scheduler
...

We can verify our properly installed dependencies by running a pip list. The resulting list shows the dependencies we’ll need.

(python-venvs) ~/demo$ pip list

Package            Version
------------------ -------
…
redis              4.4.0  
rq                 1.11.1 
rq-scheduler       0.11.0 
sendgrid           6.9.7  
…

3. Ensure Redis server is installed and running

The rq and redis Python modules will install as dependencies with the rq-scheduler. However, these modules depend on installing Redis on your local machine. So if you need to install Redis, do so, then run the following command:

(python-venvs) ~/demo$ wget \
  https://github.com/redis/redis/archive/7.0.7.tar.gz && \
  tar xzf 7.0.7.tar.gz && \
  cd redis-7.0.7 && make

Ensure the Redis server is up and running—either as a foreground process in a separate terminal window or as a background daemon service. To start up the Redis server manually, do the following:

(python-venvs) ~/demo$ ./redis-7.0.7/src/redis-server

Now that we’ve installed all our dependencies, we can begin working on our demo application.

Steps for using Python and Twilio SendGrid to send automated emails

Follow these steps to enable your Python application to use the SendGrid API for sending emails, starting by creating an API key for authentication.

1. Sign up for SendGrid and create an API key

After creating and logging into your SendGrid account, navigate to Settings > API Keys.

SendGrid settings menu

Click on Create API Key. Provide a name for the API key. However, to keep the API key privileges minimal, select Restricted Access.

SendGrid API Key Permissions dialog box

Then, under Access Details, turn on access for Mail Send.

SendGrid API Key Access Details dialog box

Click on Create & View to complete the creation of your API key. However, don’t forget to copy the value of your new API key before proceeding.

SendGrid API Key Created dialog box

We’ll need this API key in our Python application. However, referencing this API key as an environment variable is a more secure approach than hard coding it into your Python code. So set a new environment variable called SENDGRID_API_KEY, giving it the value you just copied from SendGrid.

(python-venvs) ~/demo$ export \
  SENDGRID_API_KEY=SG.DFimvXbkQHafEXnh2LlKoA.***************************

If you need help with setting environment variables, we have a useful tutorial.

2. Send an email with Python

Now that you have a SendGrid API key, you're ready to dive into some code and send emails. Let’s start by verifying that we can send emails through the SendGrid API.

In your project folder, create a new file called send_email.py with the following code:

import os
from sendgrid import SendGridAPIClient
from sendgrid.helpers.mail import Mail

message = Mail(
    from_email='your-sendgrid-account-email@example.com',
    to_emails='to@example.com',
    subject='Sending with Twilio SendGrid is Fun',
    html_content='<strong>and easy to do anywhere, even with Python</strong>')

sg = SendGridAPIClient(os.environ.get('SENDGRID_API_KEY'))


response = sg.send(message)


print(response.status_code, response.body, response.headers)

However, before running this code, remember to replace the from_email value with an address for a verified sender identity for your SendGrid account and the to_emails value with an email address that you can access. If the SendGrid API key environment variable is correct, this code should work.

Note that in production applications, you should verify your sender identity by completing domain authentication. A sender identity represents your “from” email address—the address your recipients see as the sender of your emails. For a step-by-step tutorial, check out How to Set Up Domain Authentication for Twilio SendGrid.

Use the following command to run your Python code:

(python-venvs) ~/demo$ python send_email.py

If your test send was successful, you’ll see a 202 HTTP response code. Then, check your inbox to verify you received the email.

Test email

However, if running the Python script yielded an error, these troubleshooting tips may help you:

  • 401 response: If you received a 401 response, it’s likely that your SendGrid API key was invalid. Ensure that you copied the entire key correctly and have set the SENDGRID_API_KEY environment variable in this terminal window.
  • 403 response: If you received a 403 response, it’s possible that the from_email address you’re using is not a verified sender identity for your SendGrid account. Ensure that you used the correct email address or go through these steps for single sender verification.

With our email-sending capability verified, we can build on top of this to incorporate scheduled automation with the rq-scheduler.

3. Schedule a task with RQ Scheduler

You can use the rq-scheduler to execute specific code at a specific time by creating a Scheduler object and passing it a function to execute, a Python datetime, and any arguments you want to pass to the function.

For example, we’ll create a module log_to_tmp.py that writes the current time stamp to a file in /tmp. Our code looks like this:

from datetime import datetime

def log_to_tmp():
    f = open('/tmp/rq-test.log', 'w')
    f.write("Writing at " + str(datetime.now()))
    f.close()

Then, we have our main program in main.py:

from datetime import timedelta
from redis import Redis
from rq_scheduler import Scheduler
from log_to_tmp import log_to_tmp

scheduler = Scheduler(connection=Redis())
scheduler.enqueue_in(timedelta(seconds=30), log_to_tmp)

In a separate terminal window, we need to start up the rq-scheduler.

(python-venvs) ~/demo$ rqscheduler --verbose
17:43:45 Registering birth
17:43:45 Entering run loop
17:43:45 rq:scheduler_instance:b273b502213e43578d630d: Sending a HeartBeat
17:43:45 rq:scheduler_instance:b273b502213e43578d630d: Acquired Lock
17:43:45 Checking for scheduled jobs
17:43:45 rq:scheduler_instance:b273b502213e43578d630d: Sending a HeartBeat
17:43:45 rq:scheduler_instance:b273b502213e43578d630d: Lock Removed
17:43:45 Sleeping 60.00 seconds
…

The RQ Scheduler will check Redis for scheduled jobs. Once it finds jobs ready to execute, it queues them up with RQ. This is why we need to ensure an RQ worker is also running to perform the jobs in the queue.

Note the following caveats for running your RQ worker:

  • The rqworker must launch from the folder where you house your send_email.py module. In our example, this is the ~/demo folder where we put all our code.
  • The rqworker must also have access to the SENDGRID_API_KEY environment variable. Before starting up the rqworker, ensure you set the environment variable in the terminal window where you’ll run the rqworker.
(python-venvs) ~/demo$ rqworker
17:43:31 Worker rq:worker:9a0e77e55cbe40a989f: started, version 1.11.1
17:43:31 Subscribing to channel rq:pubsub:9a0e77e55cbe40a989f
17:43:31 *** Listening on default...

Then, we run our Python program:

(python-venvs) ~/demo$ python main.py

Within a few minutes, the RQ Scheduler sees it’s time to enqueue the job:

17:44:45 Checking for scheduled jobs
17:44:45 Pushing log_to_tmp.log_to_tmp(b86101cf-2d28-4a1f-a4ca-b39b7ccbb1d8) to default
17:44:45 rq:scheduler_instance:b273b502213e43578d630d: Sending a HeartBeat
17:44:45 rq:scheduler_instance:b273b502213e43578d630d: Lock Removed
17:44:45 Sleeping 59.99 seconds

Next, the RQ worker detects a new job in the queue and performs it:

17:44:45 default: log_to_tmp.log_to_tmp() (b86101cf-2d28-4a1f-a4ca-b39b7ccbb1d8)
17:44:45 default: Job OK (b86101cf-2d28-4a1f-a4ca-b39b7ccbb1d8)
17:44:45 Result is kept for 500 seconds

When we check our TMP file, this is what we see:

(python-venvs) ~/demo$ cat /tmp/rq-test.log
Writing at 2022-12-29 17:44:45.516249

We’ve successfully verified that we can schedule tasks with the RQ Scheduler. Now, we’re ready to schedule automated emails.

4. Create a send_email module

First, we’ll encapsulate our original email sending function into a module so we can pass that function to the Scheduler object. We do this by modifying the code from the send_email.py and putting it in a function:

import os
from sendgrid import SendGridAPIClient
from sendgrid.helpers.mail import Mail

def send_email(from_email, to_email):
    message = Mail(
        from_email=from_email,
        to_emails=to_email,
        subject='Sending with Twilio SendGrid is Fun',
        html_content='<strong>and easy to do anywhere, even with Python</strong>')
    
    sg = SendGridAPIClient(os.environ.get('SENDGRID_API_KEY'))
    
    response = sg.send(message)
    
    print(response.status_code, response.body, response.headers)

Then, we update our main.py program, which will schedule this function so that it looks like this:

from datetime import timedelta
from redis import Redis
from rq_scheduler import Scheduler
from send_email import send_email

scheduler = Scheduler(connection=Redis())

if __name__ == '__main__':
    scheduler.enqueue_in(
        timedelta(seconds=30),
        send_email,
        'from_email@example.com', 'to_email@example.com')

Just as you did with the previous email-sending attempt, replace the from_email argument with your SendGrid account email address and the to_email argument with an email address that you can access.

In our example, we used timedelta and called enqueue_in() to schedule our email to send in 30 seconds. For testing purposes, you can also use enqueue_at() and supply an absolute time, such as datetime.now(), to schedule the email for immediate sending.

After ensuring you have your Redis server, RQ Scheduler, and RQ worker all running, you can run your code to schedule an email:

(python-venvs) ~/demo$ python main.py

Then, after approximately a minute, your email should send. Check your email inbox to verify you received it.

Note that if you’re running on iOS, you may encounter an error involving __NSCFConstantString initialize. This relates to multiprocessing and fork processes in Python. However, there’s a quick fix.

Success! You now have all the building blocks in place to automate email sending from within a Python application.

What's next?

In this tutorial, we discussed how to use the RQ Scheduler to schedule and automate email sending with SendGrid. Now you can use the RQ Scheduler for all your Python email automation needs, such as sending a notification when the International Space Station flies by a location.

You can also connect your Python application to webhook integrations for event-based triggering and schedule more complex tasks than just simple email sending. For example, at the scheduled time, your email sending module can make requests to gather up-to-date information for inclusion in the email body, or ensure certain conditions exist before sending the email.

Engage more customers with Twilio SendGrid and Twilio Programmable Messaging

Now that you know how to send automated emails with Twilio SendGrid and Python, why not experiment with sending SMS using Twilio Programmable Messaging?

Read more about what you can achieve with these channels in our guide Using Email and SMS to Engage Your Customers. Then, sign up for a free Twilio account to get started.