What the verifier checks#
Type an address and in a second you know whether it is worth emailing. The tool checks:
- Format: whether the address follows the rules (something like
name@domain.com), with no spaces, commas or two@. - Typos in the big providers:
gmial.com,gmail.co,hotmail.con,hotmial.com,outlok.com. When it looks like a typo we show the fixed address ("Did you mean ana@gmail.com?"). - Whether the domain receives email: we look up the MX record in DNS. Without an MX (and without an address record standing in for it), no message arrives, and every send bounces.
- Disposable inbox: temporary mailbox services that vanish in minutes. We compare against a public list of almost 10,000 domains.
- Shared mailbox: addresses such as
info@,sales@andbilling@. They work, but they are not one person's. - Free provider: Gmail, Outlook, Yahoo, iCloud and others.
How to read the result#
| Result | What it means | What to do |
|---|---|---|
| Valid | right format and the domain receives email | go ahead |
| Risky | likely typo, disposable inbox or DNS did not answer | confirm with the person first |
| Invalid | wrong format or the domain receives no email | do not send: it will bounce |
Why we never probe the mailbox#
Some verifiers connect to the recipient's server and pretend to send, just to see whether the mailbox exists. We do not, on purpose:
- Big providers (Gmail, Outlook, Yahoo) treat connections that never send as spammer behavior. The IP doing it loses reputation, and reputation is what gets email delivered.
- Many servers say "yes" to any address (catch-all) or refuse every unknown connection. The probe misleads both ways.
- Typos, domains without email and disposable inboxes, which this tool catches, are most of the bad addresses on a sign-up form.
If the format is right and the domain receives email but the mailbox does not exist, the first send comes back as a hard bounce (code 550 5.1.1). A good sending service such as Couryo puts that address on the suppression list at once and never tries again.
Use it on your sign-up form#
The best place to verify is the sign-up form, before sending the confirmation email. The person fixes their own address on the spot, and you spend no sends or reputation on bounces. The same check is on the API, no key needed:
curl "https://api.couryo.com/v1/tools/verify-email?email=ana@gmial.com"Without a key you get 50 verifications a day per IP. With any Couryo key, a free account's included, 2,000 a day. The answer fields are in the free tools docs.
For AI agents, the verify_email tool is on Couryo's public MCP server, no login: https://mcp.couryo.com/tools.
What to do with an email that bounced#
- Address does not exist (550 5.1.1): remove it and never send again.
- Mailbox full (452 4.2.2): temporary; if it repeats for days, stop mailing it.
- Policy refusal (5.7.x): the address exists, the provider blocked you. Check SPF, DKIM and DMARC with the domain checker.
Paste the error into the SMTP error explainer to understand each case, or read the SMTP error codes guide.
FAQ#
Is the email verifier really free?#
Yes. On the site and on the API without a key you get 50 verifications a day per IP. With a free Couryo account your key unlocks 2,000 a day. No card required.
Do you store the emails I verify?#
No. The address is checked and discarded. We only keep a counter per IP or account to apply the daily limit.
Why can a valid address still bounce?#
Because the mailbox itself is not probed: the domain receives email, but that person may not exist. The first send shows it, with a 550 5.1.1 bounce. Probing mailboxes on the recipient's server hurts the prober's reputation, so we do not do it.
What is a disposable email?#
A throwaway inbox created in seconds and deleted in minutes or hours. Fine for testing, but on a customer sign-up it almost always means someone who does not want to hear from you.
Can I verify a whole list?#
Through the API, yes: one call per address, up to 2,000 a day with a free key. For bigger lists start with the most recent contacts; old addresses that never opened anything deserve a re-confirmation campaign first.