How to check an email address is valid before you send

A single mistyped character sends an important email nowhere. On a mailing list, bad addresses cause bounces that can harm how reliably your mail is delivered. Checking addresses first catches most problems before they cost anything.

What a valid address looks like

• Exactly one @.
• Before it, up to 64 characters: letters, digits, dots and a few symbols such as + and _.
• No dot at the start or end of that part, and no two dots in a row.
• After it, a domain made of letters, digits and hyphens, with a real ending such as .com.
• At most 254 characters in total.

Check addresses step by step

1. Paste one address, or a whole list with one per line, into the Email Address Validator.
2. Read the result for each: valid, or what is wrong, in plain words.
3. Accept the suggested fix for likely typos in common domains.
4. Optionally check the domains' mail servers.

The format check runs in your browser. The optional mail server check sends only the domain names — the part after each @ — to this site's server for a DNS lookup, never the full addresses.

Things that are valid, though people doubt it

• Plus addressing, such as jane+newsletter@example.com. Many providers deliver it to jane@example.com, and it is useful for filtering. Some websites wrongly reject it.
• Capital letters. Domains are not case-sensitive, and in practice almost every provider treats the part before the @ the same way.
• Long domain endings such as .photography or .international.

Does the domain receive email?

A domain's MX records say which servers accept its email. The mail server check looks them up and tells you whether the domain can receive mail, has declared that it accepts none, or does not exist at all — which catches addresses at mistyped or defunct domains.

Typos worth catching

Most bad addresses are not malformed; they are mistyped. The validator flags likely typos in common domains — the kind of slip that turns gmail.com into gmial.com or gmail.con, or drops the dot before the ending. Such an address may be perfectly well formed, and even point at a real domain someone has registered, so it is worth confirming with the person rather than silently correcting it. On sign-up forms, showing a “did you mean…?” suggestion at the moment of typing prevents most of these.

What validation cannot prove

A correctly formed address at a working domain can still belong to no one. The only way to know a particular mailbox exists is to send it a message. Many mail servers accept every address at first and bounce later, and probing mailboxes one by one is unreliable and treated as abuse. That is why sign-up forms send a confirmation email: it proves the address works and that its owner agreed.

Cleaning a list

1. Tidy stray spaces and invisible characters with Text Cleaner.
2. Remove duplicates with Remove Duplicate Lines, with case sensitivity off.
3. Validate the list and fix or remove what fails.

Only email people who have agreed to hear from you. A clean list of people who asked to be on it is worth far more than a long list of addresses gathered elsewhere — and in many countries the law requires consent.