Email verification checks whether an email address is real and can receive mail, without sending it anything. For cold email it's essential: every hard bounce costs your sending domain some reputation.
What a verifier checks
- Syntax: the address is written correctly.
- Domain: the domain exists and has an MX record.
- Mailbox: the mail server says the mailbox exists, by starting a delivery and stopping before any email is sent.
- Risk flags: catch-all domains, disposable addresses and role-based addresses.
Reading the results
Send to valid addresses. Remove invalid ones. Treat catch-all and unknown with care: they can't be confirmed, so send to them in small numbers or not at all.
When to verify
Right before sending, even if the list was verified when you got it: addresses die every month. Keep the bounce rate under 2%. mailzy's Email Verifier checks one address or a whole CSV, refunds every unknown result, and gives your first 100 checks free.