What’s the difference between syntax and domain validation?

Syntax validation checks format correctness: proper structure (local@domain), allowed characters, and RFC compliance. It catches obviously invalid addresses like missing @ symbols or illegal characters. Fast and deterministic but limited.

Domain validation verifies the domain exists and accepts email: **DNS** resolution, **MX record** presence, and domain configuration. It catches addresses at non-existent or non-mail domains. Requires **DNS** queries but still fast.

Neither confirms the specific mailbox exists. An address can pass both checks yet bounce because the specific user doesn't exist. Deeper verification requires mailbox-level checking, which adds complexity and limitations.