Email validator

Three layers, all without sending mail. Syntax: the address is tested against a practical subset of RFC 5322, catching missing @ signs, illegal characters, and double dots. Domain: a live MX lookup confirms the domain publishes mail servers, which filters out typo domains like gamil.com that syntax checks pass. Provider: the domain is compared against curated lists of free consumer providers and known disposable services.

The one thing no browser tool can check is whether the specific mailbox exists. That requires an SMTP conversation with the receiving server, and mainstream providers deliberately obscure the answer to prevent address harvesting.

Validate at the point of capture: a signup form that checks syntax and MX before accepting an address prevents most bad data from entering your system, cheaper than bouncing later. Blocking disposable domains at signup is standard for products that gate features by account.

Validation is not a substitute for bounce handling. Addresses go stale, so your sending pipeline still needs to process bounces and suppress dead addresses, both to protect your sender reputation and because providers throttle senders with high bounce rates.