Day 20 of a serverless tutorial moves beyond basic SMS alerts to user-facing HTML emails using Amazon SES. While SNS handles plain text well, SES provides the structure needed for rich MIME types. The guide walks through verifying an email identity in the SES console and adding the correct IAM permissions to a Lambda function.

The Python code requires a dictionary structure, unlike SNS's simple string input. Developers must specify source, destination, and a message body containing both HTML and Text parts. A pro tip recommends using inline CSS for email templates, since major clients like Gmail and Outlook frequently strip external stylesheets, which can break email formatting.

This approach is essential for transactional emails like receipts or notifications. The shift from SNS to SES reflects a common architectural pattern where AWS Lambda handles backend logic while SES manages scalable email delivery. Developers should test thoroughly in SES's sandbox before requesting production access to avoid deliverability issues.