MailChecker is a cross-platform library for determining whether an email address is from a disposable or temporary email provider. It is implemented in 10+ languages (Node.js, PHP, Python, Ruby, Rust, Go, Java, Elixir, Clojure, etc.) via a centralized template-based code generation system. The library's core is a curated blacklist of over 55,000 disposable email domains stored in a plain text file (`list.txt`). Each platform provides a tiny API: `isValid(email)` returns `true` if the email format is valid AND its domain is not in the blacklist, and `blacklist()` to retrieve the domain list. The code generation pipeline (`lib/generator.js`) uses Mustache templates (`*.tmpl.*`) to produce optimized platform-specific code. The repository also includes domain cleanup scripts and comprehensive per-platform tests run in Docker containers. This is a purely application-oriented library; it does not contain data pipelines, ML models, or research artifacts.