Email syntax checker
Most syntax validators are either a regular expression that rejects valid addresses or one that accepts nonsense. This applies the rules receivers really enforce, and says which parts of the standard are technically legal and practically unusable.
Free, no signup, no daily limit. We do not store what you check here.
The standard is wider than reality
RFC 5321 permits quoted local parts containing spaces, comments in parentheses, and addresses that would make most software fail. Almost no mail provider accepts them at registration, and a great deal of software downstream mishandles them. So an address can be simultaneously standards-compliant and a mistake to accept — which is why a checker that only reports "valid per the RFC" is not answering the question anybody asked.
What syntax can never tell you
That a well-formed address exists. Syntax rules out the impossible and says nothing about the rest, and the overwhelming majority of bounced mail goes to addresses that were perfectly well formed. If you are checking a list before sending, syntax is the cheap first pass that removes typos; it is not the check that saves you from a bounce.
Questions
Should I accept addresses with a plus sign?
Yes. Rejecting them is a common bug and a real annoyance — subaddressing is how many people organise mail, and the address is entirely valid.
What about new domain endings?
Accept them. Rules that check against a fixed list of endings break every time the list grows, and they have been breaking for over a decade now.
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When you need more than a free tool
This page answers what can be determined offline and from public DNS. The API adds live carrier and mailbox verification, a calibrated confidence score, and the full evidence trail behind every verdict.
Credits never expire. Inconclusive verdicts are never billed. Cancel in one call. See pricing or read the docs.