Trouble sending emails through Flask-Mail using Heroku and Mailgun SMTP

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1

I’m having issues with my Flask app on Heroku. It’s supposed to send emails via Mailgun’s SMTP service but nothing’s happening. Here’s what I’ve got:

from flask import Flask
from flask_mail import Mail, Message
import os

app = Flask(__name__)
mail = Mail(app)

app.config.update(
    MAIL_SERVER=os.environ.get('MAILGUN_SMTP_SERVER'),
    MAIL_USERNAME=os.environ.get('MAILGUN_SMTP_LOGIN'),
    MAIL_PASSWORD=os.environ.get('MAILGUN_SMTP_PASSWORD'),
    MAIL_USE_TLS=True
)

def send_test_email(recipient):
    msg = Message('Test Email', 
                  sender='[email protected]',
                  recipients=[recipient])
    msg.body = 'This is a test email.'
    mail.send(msg)

@app.route('/test-email')
def test_email_route():
    send_test_email('[email protected]')
    return 'Email sent (supposedly)'

if __name__ == '__main__':
    app.run(debug=True)

The app runs fine and says the email was sent but nothing shows up in my inbox. What am I missing? How can I debug this? Thanks for any help!

2

I encountered a similar problem when deploying my Flask app on Heroku with Mailgun. Have you verified that your Mailgun domain is properly set up and active? Sometimes, the domain needs to be validated before you can send emails. Also, double-check your Mailgun API credentials - even a small typo can cause silent failures.

Another thing to consider is Heroku’s ephemeral filesystem. If you’re trying to send attachments or using any file-based operations in your email sending process, that could be causing issues. Lastly, try implementing some logging in your send_test_email function to capture any exceptions. This can provide valuable insight into what’s going wrong behind the scenes.

3

hey john, i’ve had similar issues. check ur heroku logs for any error messages. also, make sure ur environment variables are set correctly in heroku’s config vars. sometimes the issue is with mailgun’s free tier limits - u might wanna check that too. good luck!

4

I’ve dealt with this exact problem before. One thing that’s not immediately obvious is that Heroku’s free tier goes to sleep after 30 minutes of inactivity. This can cause issues with background tasks like sending emails.

To troubleshoot, I’d suggest adding some logging to your send_test_email function. Something like:

import logging
logging.basicConfig(level=logging.DEBUG)

def send_test_email(recipient):
    try:
        msg = Message('Test Email', 
                      sender='[email protected]',
                      recipients=[recipient])
        msg.body = 'This is a test email.'
        mail.send(msg)
        logging.info('Email sent successfully')
    except Exception as e:
        logging.error(f'Failed to send email: {str(e)}')

This will give you more information about what’s happening when the function is called. Also, consider using a task queue like Celery for sending emails asynchronously. This can help avoid timeouts and ensure your emails get sent even if your dyno goes to sleep.