|> Building an email newsletter application using Express, Node.js, and SendGrid can help businesses connect with their audience and build engagement. The application allows users to sign up for a newsletter, confirm their subscription via a unique confirmation link sent to their email inbox, unsubscribe from the list through a custom link at the bottom of every email newsletter, and upload an HTML file to send out newsletters to all subscribers on the list. The application uses SendGrid's Marketing Campaigns feature to manage contacts and lists without needing to set up a database. It also uses the SendGrid API to verify the sender identity, generate API keys, create contact lists, and add custom fields. The application is built using Node.js, Express, and EJS templates, and uses Nodemon to automatically restart the server when file changes are detected.