Checking if an email address exists means confirming that a real mailbox is active at that domain. This prevents sending to non-existent addresses, which causes hard bounces and damages your sender reputation.
Steps to Check If an Email Exists
1. Run a syntax check
Confirm the address structure is valid before doing any network lookups. Invalid syntax always means the address does not exist.
2. Look up the domain MX record
Use DNS to find the mail servers for the domain. If no MX record is found, the domain cannot receive email and the address does not exist in any useful sense.
3. Connect via SMTP
Open a connection to the mail server and send: EHLO, MAIL FROM, and RCPT TO. The server response tells you whether the mailbox is accepted (250) or rejected (550). This is the definitive check.
4. Handle special cases
Catch-all servers accept any address regardless of whether the mailbox exists. In this case, mark the address as "catch-all" rather than confirmed valid. Disposable email services create temporary mailboxes that technically exist but are worthless for marketing.
Tips
- Never send cold email to addresses you have not verified тАФ ISPs will flag you.
- A hard bounce = a non-existent address. Remove it immediately.
- Use the BillionVerify API at signup forms to check in real time.