How to check if an email address exists
Every email address belongs to a mail server, and that server knows which mailboxes it has. Email verification simply asks it.
The checker starts a normal email delivery: it connects to the mail server of the domain and says "I have an email for jane@acme.com". The server answers yes or no. Then the checker hangs up before anything is sent. The person never receives anything and never knows the check happened.
Before that, it checks the basics: that the address is well formed and that the domain exists and is set up to receive email. A typo in the domain is the most common reason an address does not work.
What the email verification results mean
Every address comes back with one of four results.
- Deliverable. The mail server confirmed the mailbox exists. Safe to send.
- Undeliverable. The mailbox or the domain does not exist. Sending to it means a bounce.
- Risky. The address may work, but something is off: a catch-all domain that accepts every address, a disposable inbox, a full mailbox. Send with care.
- Unknown. The mail server did not give a clear answer, which happens with some providers that protect their users from this kind of check. Neither good nor bad.
What is a catch-all email domain?
Some companies set their mail server to accept email for any address at their domain, so nothing sent to them is lost. jane@acme.com, j.doe@acme.com and anything@acme.com all get a yes.
That is convenient for them, and frustrating for verification: when every address is accepted, no single one can be confirmed. That is why a catch-all address comes back as risky rather than deliverable. Most of the time it reaches someone, but some of those emails end up in a mailbox nobody reads.
Why verify email addresses before sending
Every email sent to an address that does not exist bounces. Inbox providers count bounces: when they go above a few percent, Gmail and Outlook start treating your domain as careless, or as a spammer. Your emails to real customers then land in spam too.
Lists decay faster than people think. People change jobs, companies close, addresses get mistyped at sign-up. A list that was clean a year ago can easily have 10 to 20% of dead addresses today.
Verifying an address before you send is the cheapest way to protect your sender reputation. And if your emails still struggle to reach the inbox, check the setup of your domain with our free Deliverability Setup Checker.
When to use an email checker
A few moments when checking an address is worth it.
- Before emailing someone for the first time, especially an address you found or guessed.
- Before a campaign to an old list you have not emailed in months.
- When an address looks wrong, like a sign-up from a domain you have never seen.
- After finding an address with a permutator, to know which of the guesses is the real one.