Automate e-mail sending from Heroku with Python

Add Mailgun to the add-ons (there are other options, but this one was for me the easiest to configure). You can do it via the CLI with:

heroku addons:create mailgun:Starter 

Or you can do it via the user-interface via resources and in the add-ons input typing Mailgun:

See your heroku mailgun variables in the CLI with:

heroku config

You will see something like this:

MAILGUN_API_KEY:         123..
MAILGUN_DOMAIN:          sandbox123...
MAILGUN_PUBLIC_KEY:      pubkey-123...
MAILGUN_SMTP_LOGIN:      postmaster@sandbox123...123.mailgun.org
MAILGUN_SMTP_PASSWORD:   abcd123
MAILGUN_SMTP_PORT:       587
MAILGUN_SMTP_SERVER:     smtp.mailgun.org

Copy and paste this into a file with the name mailgun.py

import smtplib
from email.mime.text import MIMEText

def send_message_mailgun(text, subject, recipient, sender, smtp_login, password, smtp_server, port):
    msg = MIMEText(text)
    msg['Subject'] = subject
    msg['To'] = recipient
    msg['From'] = sender
    s = smtplib.SMTP(smtp_server, port)
    s.login(smtp_login, password)
    s.sendmail(msg['From'], msg['To'], msg.as_string())
    s.quit()

In your main.py or another python script from which you want to send the mail, add your e-mail recipient, text and subject and add references to Mailgun variables:

from mailgun import send_message_mailgun

text = "your message"
subject = "subject of message"
recipient = "myself@email.com"
sender = "foo@" + str(os.environ["MAILGUN_DOMAIN"])
smtp_login = str(os.environ["MAILGUN_SMTP_LOGIN"])
smtp_server = os.environ["MAILGUN_SMTP_SERVER"]
password = os.environ["MAILGUN_SMTP_PASSWORD"]
port = int(os.environ["MAILGUN_SMTP_PORT"])
send_message_mailgun(text, subject, recipient, sender, smtp_login, password, smtp_server, port)

The mail will most likely end up in the spam box of the recipient so the sender address needs to be unspammed in the email account of the recipient.