Email validator

How this inspector works

The tool runs four independent checks and combines them into a single score. Three of them happen entirely in your browser. Only the fourth, the MX lookup, leaves your device, and it sends nothing but the domain part of the address.

Syntax against RFC 5322

The internet message format specification, RFC 5322, defines what an address may legally contain. The local part before the @ can hold letters, digits and a set of printable symbols, or a quoted string for the unusual cases. It cannot start or end with a dot, cannot contain two dots in a row, and cannot exceed 64 characters. The domain part has to be a sequence of labels separated by dots, each label up to 63 characters, ending in a top level domain of at least two letters. The whole address is capped at 254 characters by the SMTP path limit in RFC 5321. When a check fails here, the inspector names the specific rule rather than returning a bare invalid, because the fix is usually obvious once you know which rule you broke.

MX records over DNS-over-HTTPS

A mail exchanger record tells the sending world which servers accept mail for a domain. A domain with no MX record cannot receive mail, so every address at that domain will hard bounce. Browsers cannot open a DNS socket or talk to port 25, so the lookup uses DNS-over-HTTPS, an HTTPS endpoint that returns DNS answers as JSON. The query goes to Google's public resolver. If your network blocks that endpoint, the tool retries through this site's own resolver and tells you which source answered. Records are listed by priority, lowest first, which is the order a sending server tries them.

Role accounts and disposable domains

Addresses like admin@, info@ and support@ reach a shared inbox rather than a person. They convert poorly, they are frequently monitored by abuse teams, and some of them are spam traps. They are not invalid, so they are flagged rather than rejected. Disposable domains are a different problem: the mailbox is real today and gone next week. The inspector matches against an embedded list of known throwaway providers, which catches the common ones without sending your address anywhere.

Typo correction

Domain typos are checked two ways. A table of known misspellings catches the frequent ones directly, and an edit distance comparison against the major consumer providers catches the rest. A suggestion appears when a domain is within two character edits of a real one and of a similar length, which keeps the false positives down.

What the score means, and what it cannot tell you

The score adds points for each problem found: unparseable syntax, a missing MX record, a disposable domain, a role mailbox, a likely typo, and a few smaller signals. Zero means nothing raised a flag. It does not mean the mailbox exists. Confirming that requires an SMTP handshake with the receiving server, and most large providers now accept every recipient during that conversation and bounce later, so a live check would give a confident answer that is often wrong.

Bulk CSV and the three verdicts

The bulk tab runs the same checks over a whole file. Your CSV is parsed on the server, the email column is found by header name or, when there are no usable headers, by looking for address-shaped values in the first rows, and every row goes through syntax parsing, the disposable list and an MX lookup. Rows are processed through a bounded pool of concurrent lookups with DNS answers cached per domain, so a list of two thousand contacts at one company costs one lookup rather than two thousand.

Each row comes back as one of three verdicts. Invalid means the address cannot receive mail: the syntax fails, the domain publishes no MX record, or the domain is a throwaway provider. Valid means the syntax passes and the domain is hosted by a provider that rejects unknown recipients, so an address that survives is very likely real. Catch-All means the domain accepts mail but the individual mailbox cannot be confirmed from DNS, which is the honest answer for most company domains. Your original columns are preserved and two are appended, Validation_Status and Validation_Reason, so you can always see why a row was judged the way it was.

Privacy

The address you type is not logged, stored or transmitted anywhere except as the domain part of a DNS query. There is no account, no upload, and no list building. Closing the tab discards everything.

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