UserCheck is an advanced real-time email validation API designed to identify and prevent the use of disposable, temporary, and potentially fraudulent email addresses and domains, allowing applications to concentrate on authentic users while minimizing fake registrations and misuse. It assesses the validity, activity, and reliability of both email addresses and domains, evaluates domain reputation, recognizes public email providers, relays, and role accounts, and provides intelligent recommendations for typical misspellings, syntax checks, and the ability to process extensive lists in bulk. UserCheck consistently refreshes its database of disposable emails and refines its validation protocols, offering smooth integration through a straightforward REST API that delivers predictable JSON responses for streamlined, low-latency verification processes. It is capable of scaling up to accommodate high request volumes without compromising performance quality and includes features for organizing workflows across different environments such as development, staging, and production. Furthermore, it boasts additional functionalities like customizable blocklists, support for webhooks, and seamless integration with various tools, enhancing its versatility in diverse applications. This makes UserCheck a comprehensive solution for ensuring the integrity of email interactions within digital platforms.