The Lob API enables users to programmatically send physical mail at scale, catering to various business needs such as marketing, healthcare communications, and invoice delivery, as exemplified by companies like Counsyl and Amazon. The API offers distinct services for postcards, letters, checks, and address verification, with an emphasis on developer-friendliness through features like automatic Webhook tracking of mail progress and HTML-based mail design. Built initially in PHP, Lob transitioned to Node.js using the hapi.js framework for improved efficiency and response times, leveraging AWS Lambda for rendering tasks. The API is accessible via RapidAPI, where users can test its capabilities with ease, and it is particularly appreciated for its straightforward setup and developer-centric design.