How to verify email addresses at signup

What an address check can tell you

• Syntax: is it shaped like an email address at all?
• The domain: does it exist, and does it publish a mail server (an MX record)? user@no-such-domain-xyz.com fails here.
• Throwaway providers: addresses from temporary-mailbox services that are meant to be discarded.
• Role addresses: info@, admin@, sales@. They reach a group, not a person, so they bounce and complain more.
• Likely typos: maria@gmial.com is almost certainly gmail.com.

What it cannot tell you

Whether that exact mailbox exists. Many mail servers accept every address and only bounce the message later, so no honest tool can promise a mailbox is real. That is why verification is the first filter, not the last: it removes the obvious problems, and a confirmation email proves the rest.

Where to put it

1. In the browser, when the field loses focus. If the check suggests a fix, show it kindly: “Did you mean maria@gmail.com?” with a one-click button. Do not block the person for a role address or a throwaway one if you can avoid it. Explain, and let them continue.
2. On your server, when the form is submitted. Never rely on the browser check alone. Anyone can skip it.
3. Then send a confirmation email and treat the account as unconfirmed until the link is used. That is the real proof.

Do it with SendSend

SendSend has an address-checking API, with the checks above, a plain verdict (valid, invalid, risky or unknown) and a suggested fix for typos. You can send one address at a time or up to 100 in a batch. Try it without an account on the free email checker, or read the guide.

A few habits

• Check on the way in, and again before you send a large campaign to an old list.
• Keep the message friendly. A person who mistyped does not need a red error.
• Do not store addresses you rejected longer than you need to.