Configuring and Sending Emails in Domino Using Python smtplib

Issue

Users need guidance on how to send emails from Domino using Python’s smtplib library, including how to set up a secure SMTP connection, send plain-text emails, and send HTML-formatted emails using MIME.

Root cause

Sending emails from Domino requires configuring a secure SMTP connection and using the correct Python libraries. Without proper setup of connection security, authentication, and MIME formatting, emails may fail to send or render incorrectly.

Resolution

This article covers three topics:

Setting up a secure SMTP connection using SMTPS or STARTTLS
Sending plain-text emails using smtplib
Sending HTML-formatted emails using the email.mime module

1. Setting up a local SMTP debug server

To test your code locally, use the Python smtpd binary bound to port 1025. Messages will not leave localhost and will be output to stdout as a byte stream:

python -m smtpd -c DebuggingServer -n localhost:1025

2. Starting a secure SMTP connection

There are two ways to secure your SMTP connection. Both examples use Gmail’s SMTP server and Python’s ssl package to load the system’s default trusted CA bundles via create_default_context(). Option A: SMTPS (secured from the outset)

# Using SMTPS to secure the connection from the outset
import smtplib, ssl

port = 465  # For SSL
password = input("Input password and press enter: ")

# Create a secure SSL context, loads system's default trusted CAs
context = ssl.create_default_context()

with smtplib.SMTP_SSL("smtp.gmail.com", port, context=context) as server:
    server.login("my@gmail.com", password)

Option B: STARTTLS (connection secured after initial handshake)

# Using STARTTLS to secure the connection from a point onwards
import smtplib, ssl

smtp_server = "smtp.gmail.com"
port = 587  # For STARTTLS
sender_email = "my@gmail.com"  # Enter your address
password = input("Input password and press enter: ")

# Create a secure SSL context, loads system's default trusted CAs
context = ssl.create_default_context()

try:
    server = smtplib.SMTP(smtp_server, port)
    server.ehlo()  # Can be omitted, called implicitly by the method if required
    server.starttls(context=context)  # Secure the connection
    server.ehlo()  # Can be omitted, called implicitly by the method if required
    server.login(sender_email, password)
    # TODO: Send email here
except Exception as e:
    # Print any error messages to stdout
    print(e)
finally:
    server.quit()

3. Sending a plain-text email

Define the sender, receiver, and message body at the top of your script. Use server.sendmail to send the email. Using SMTPS:

import smtplib, ssl

port = 465  # For SSL
smtp_server = "smtp.gmail.com"
sender_email = "my@gmail.com"  # Enter your address
receiver_email = "your@gmail.com"  # Enter receiver address
password = input("Input password and press enter: ")
message = """\
Subject: Hi there

Message body after 2 new lines."""

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)

Using STARTTLS:

import smtplib, ssl

port = 587  # For STARTTLS
smtp_server = "smtp.gmail.com"
sender_email = "my@gmail.com"  # Enter your address
receiver_email = "your@gmail.com"  # Enter receiver address
password = input("Input password and press enter: ")
message = """\
Subject: Hi there

Message body after 2 new lines."""

context = ssl.create_default_context()
with smtplib.SMTP(smtp_server, port) as server:
    server.ehlo()  # Can be omitted, called implicitly by the method if required
    server.starttls(context=context)
    server.ehlo()  # Can be omitted, called implicitly by the method if required
    server.login(sender_email, password)
    server.sendmail(sender_email, receiver_email, message)

4. Sending HTML-formatted emails using MIME

Use the email.mime module to send emails combining HTML and plain-text content. Since email clients render the last MIME part first, the HTML part must be added after the plain-text part.

import smtplib, ssl
from email.mime.text import MIMEText  # Contains the HTML and plain-text content
from email.mime.multipart import MIMEMultipart  # Combines the two

sender_email = "my@gmail.com"  # Enter your address
receiver_email = "your@gmail.com"  # Enter receiver address
password = input("Input password and press enter: ")

message = MIMEMultipart("alternative")
message["Subject"] = "multipart test"
message["From"] = sender_email
message["To"] = receiver_email

# Create the plain-text and HTML version of your message
text = """\
Hi,
How are you?"""
html = """\
<html>
  <body>
    <p>Hi,<br>
      How are you?<br>
    </p>
  </body>
</html>
"""

# Convert these into MIMEText objects
text1 = MIMEText(text, "plain")
html1 = MIMEText(html, "html")

# Add the objects to the MIMEMultipart object
# The email client renders the last part first, hence we add the HTML part last
message.attach(text1)
message.attach(html1)

# Create secure connection with server and send email
context = ssl.create_default_context()
with smtplib.SMTP_SSL("smtp.gmail.com", 465, context=context) as server:
    server.login(sender_email, password)
    server.sendmail(
        sender_email, receiver_email, message.as_string()
    )

Notes

When configuring for a production Domino deployment (assumed to use AWS SES as the SMTP server), the following values are required:

SMTP host: The server name from the SMTP settings page, accessible via the AWS SES service page.
SMTP username and password: Generate these from the SMTP settings page using the Create My SMTP Credentials button.
These values should be available in Domino Central Config. If not, they must be added as Central Config key-value pairs. Contact your internal Domino admin for assistance.
The code examples in this article are provided as a reference. Some adjustments and indentation corrections may be needed to suit your specific application.

​Issue

​Root cause

​Resolution

​1. Setting up a local SMTP debug server

​2. Starting a secure SMTP connection

​3. Sending a plain-text email

​4. Sending HTML-formatted emails using MIME

​Notes