[email protected] passes plenty of validation logic. It's shaped exactly like an email address — an @, a domain, a TLD. It will also bounce, because the domain doesn't exist. Shape and deliverability are two different questions, and most signup forms only ever ask the first one — which means every list you haven't verified is quietly losing you money right now.
What syntax checking actually tells you
A regex or format check can confirm one thing: the string looks like an email address. It cannot tell you:
- Whether the domain has a mail server configured at all
- Whether the specific mailbox was deleted eighteen months ago
- Whether
info@on that domain bounces straight to nobody - Whether the domain is a catch-all that silently accepts every address you throw at it, valid or not
A verdict that only checks the shape of the string is worse than no verdict, because it looks like due diligence was done when none actually happened.
Why this costs more than one bounce
Sending to an address that looks fine but isn't deliverable costs you three separate things: the send itself (already paid for, on most lists), a bounce that does nothing for your open rate, and — the expensive one — a hit to your sender reputation with your ESP. Enough bad sends and your next campaign starts landing in spam for addresses that were perfectly good to begin with. One bad address is a rounding error. A list that's never been verified is a slow reputation leak — and every campaign you send before fixing it makes the damage a little harder to undo.
A regex can tell you an address is shaped correctly. Only a live mailbox probe can tell you it actually exists.
What a real check looks like
The only way to know whether a mailbox will accept mail is to ask the destination server directly — a live SMTP conversation, the same signal your own mail server would get, without actually sending anything. Combined with typo suggestion (catching gmial.com before it ever reaches a form), disposable and role-account detection, and MX resolution, that's the difference between a guess and a verdict you can act on.
Verify before your next send — not after you've already bounced
Your next campaign is already scheduled to hit some percentage of dead addresses. Every unverified send between now and when you fix that is reputation you can't get back. UptimeLuna runs every address through an eight-step pipeline — syntax, typo suggestion, disposable/role/free-provider detection, MX resolution, and a live SMTP mailbox probe — so you get a real answer instead of a regex guess. Register free and clean your list before your next send goes out.