The blog post by Gleb Bahmutov explores the process of testing HTML emails using Cypress with a local SMTP server to ensure they function and display correctly. It provides a detailed guide on setting up a testing environment using Node and the nodemailer module to send emails, and smtp-tester to receive them. Bahmutov explains how to create reusable transporter objects for sending emails and how to set up a local SMTP server to capture and log incoming messages. The post includes step-by-step instructions for testing the registration and confirmation process of an application, utilizing Cypress to automate the testing of both plain text and HTML emails. The tutorial highlights the benefits of using Cypress for testing email functionalities, offering insights into debugging and confirming that the HTML content and links within the emails work as expected. Lastly, the post suggests extending tests for better accessibility and styling consistency across different viewports, and it hints at using third-party services for email testing if needed.