What does the "Invalid" result status mean?

Invalid is the cleanest negative verdict in the Valid Email Checker enum. It tells you the address cannot receive mail right now and almost certainly never will. Send a campaign message there and it will bounce, which is exactly the outcome you bought verification to avoid.

In the canonical status set (safe, risky, invalid, unknown, catch_all, disposable, role, spamtrap, disabled, inbox_full), invalid represents structural non-existence. The mailbox is not just dormant or full — it is wrong at the protocol level.

The four reasons an address comes back Invalid

1. Syntax failure. johnnsmith@@example.com and user@.com cannot be parsed as valid email addresses. Step 1 of the 11-step engine rejects these immediately.
2. Domain does not resolve. The domain has no DNS record at all, often because of a typo (gmial.com, outlok.com) or because the domain was deleted. Step 2 catches this.
3. No MX record. The domain exists but has no mail server configured. Many parked domains and website-only domains land here. Step 3 catches this.
4. Mailbox rejection. The mail server replied to our SMTP RCPT TO probe with a definitive 550-class error confirming the mailbox does not exist. Step 5 catches this.

What to do with Invalid entries

Remove them from your list before your next send. There is no upside to retaining an Invalid entry, no second-pass strategy that recovers them, and no engagement test that would change the result. The mailbox does not exist; nothing you send reaches a human.

Some teams keep an archived copy of removed Invalid addresses for record-keeping (matching against future suppression lists, complying with retention requirements). That is fine — just keep them out of any active sending segment.

How accuracy looks for Invalid specifically

Of the categories in our 99%+ accuracy band, Invalid is the easiest to verify with certainty. A 550 mailbox-not-found response from the mail server is direct, unambiguous truth at the protocol level. There is little room for the engine to be wrong on a real Invalid, which is why this is one of the bands where the accuracy claim holds up most strongly.

The only way you can get a false Invalid is if a server is misbehaving when we probe it (sending 550 when the mailbox actually exists). VEC catches the most common variant of this by routing through fallback providers when the primary response looks suspicious.

Invalid versus Disabled and Inbox Full

Invalid means the mailbox structurally does not exist. Disabled means the mailbox once existed but has been turned off by the provider. Inbox Full means the mailbox exists and is active but cannot accept more mail right now. Each is a separate status because the recovery action differs — Invalid is permanent, Disabled is usually permanent, Inbox Full clears on its own as the recipient deletes mail.

For a full breakdown of every status the engine can return, see result types explained.