How to send Emails via Python

I've assumed that sending emails via a CLI would be easy. That might even be the case, but sending them in a way that they actually show up in the receiver's mailbox is quite a different story. After following multiple tutorials and using tools from sendmail to mailx, not a single email arrived. Since I wanted to send the mail from within a Python script anyway, I moved on to a Real Python tutorial. This is the snippet they use to send an email.

import smtplib, ssl

port = 465  # For SSL
smtp_server = "smtp.domain.com"
sender_email = "my@domain.com"      # Enter your address
receiver_email = "your@domain.com"  # Enter receiver address
password = "MY_PASSWORD"            # Enter password
message = """\
Subject: Hi there

This message is sent from Python."""

context = ssl.create_default_context()
with smtplib.SMTP_SSL(smtp_server, port, context=context) as server:
    server.login(sender_email, password)
    server.sendmail(sender_email, receiver_email, message)

And again, nothing arrived at my preferred receiver protonmail. However, if you try to email to a gmail address, you get a helpful error back.

Our system has detected that this message is not RFC 550-5.7.1 5322
compliant: 'From' header is missing. To reduce the amount of spam sent
to Gmail, this message has been blocked.

This is how the snippet looks after adding the 'From' header:

import smtplib, ssl

port = 465  # For SSL
smtp_server = "smtp.domain.com"
sender_email = "my@domain.com"      # Enter your address
receiver_email = "your@domain.com"  # Enter receiver address
password = "MY_PASSWORD"            # Enter password
# 👇 The string is now a f-string and the 'From' header has been added
message = f"""\
From: <{sender_email}>
Subject: Hi there

This message is sent from Python."""

context = ssl.create_default_context()
with smtplib.SMTP_SSL(smtp_server, port, context=context) as server:
    server.login(sender_email, password)
    server.sendmail(sender_email, receiver_email, message)

And voilà, the email arrives at gmail. Again nothing at protonmail, but now it wasn't too hard to guess that it might want a 'To' header.

import smtplib, ssl

port = 465  # For SSL
smtp_server = "smtp.domain.com"
sender_email = "my@domain.com"      # Enter your address
receiver_email = "your@domain.com"  # Enter receiver address
password = "MY_PASSWORD"            # Enter password
# 👇 The 'To' header has been added
message = f"""\
From: <{sender_email}>
To: <{receiver_email}>
Subject: Hi there

This message is sent from Python."""

context = ssl.create_default_context()
with smtplib.SMTP_SSL(smtp_server, port, context=context) as server:
    server.login(sender_email, password)
    server.sendmail(sender_email, receiver_email, message)

The Real Python tutorial is from 2018, so chances are that there are better ways to send emails nowadays. After looking through the standard library docs, I think the following snippet is a more idiomatic way to achieve the same thing in 2022. The main difference is that it removes duplication with the help of the EmailMessage class.

import smtplib, ssl
from email.message import EmailMessage

port = 465  # For SSL
smtp_server = "smtp.domain.net"
sender_email = "my@domain.at"       # Enter your address
receiver_email = "your@domain.com"  # Enter receiver address
password = "MY_PASSWORD"            # Enter password

subject = "Hi there"
content = "This message is sent from Python."

msg = EmailMessage()
msg['Subject'] = subject
msg['From'] = sender_email
msg['To'] = receiver_email
msg.set_content(content)

context = ssl.create_default_context()
with smtplib.SMTP_SSL(smtp_server, port, context=context) as server:
    server.login(sender_email, password)
    server.send_message(msg)

You can find the discussion at this Mastodon post.