The 10 fields and concepts you'll meet in the response — defined in plain English, each with a real example value.
Simple Mail Transfer Protocol—the standard protocol for sending and routing email between servers.
SMTP verification connects to a mail server and simulates sending an email to check if the address exists. The server responds with a code indicating acceptance or rejection. This is the most accurate validation method but takes 1-3 seconds per address.
ExampleSMTP response: 250 OK (address exists), 550 User unknown (invalid)
Mail Exchange records in DNS that specify which mail servers accept email for a domain.
MX records are queried during email delivery to find the correct mail server. If a domain has no MX records, it cannot receive email. Email validation checks MX records to confirm the domain is configured for email and catch typos like gmial.com.
ExampleMX record: gmail-smtp-in.l.google.com (priority: 5)
A temporary email address created for short-term use, often to avoid giving a real email address.
Services like tempmail.com, 10minutemail.com, and guerrillamail.com provide disposable addresses that self-destruct after a short period. They're used for privacy or to bypass signup requirements. Blocking disposable emails prevents fake accounts and protects email list quality.
ExampleDisposable: [email protected], Real: [email protected]
An email address assigned to a function rather than a person, like info@, support@, or admin@.
Role-based addresses are often shared mailboxes monitored by multiple people. They typically have lower engagement rates for marketing emails. Some senders exclude role-based addresses from marketing campaigns but allow them for transactional emails.
ExampleRole-based: [email protected], Personal: [email protected]
A public email service like Gmail, Yahoo, or Outlook that anyone can sign up for at no cost.
Free email providers are distinguished from corporate/custom domains. For B2B lead qualification, corporate emails ([email protected]) are often prioritized over free emails ([email protected]). However, many legitimate users use free providers.
ExampleFree: [email protected], Corporate: [email protected]
A domain configured to accept email sent to any address, even if that specific mailbox doesn't exist.
Catch-all domains route all unmatched emails to a default mailbox. This makes it impossible to verify individual addresses via SMTP because the server accepts everything. Small businesses commonly use this configuration.
Example[email protected] will be accepted
Sender Policy Framework—a DNS record that lists which mail servers are authorized to send email for a domain.
SPF prevents email spoofing by letting domain owners specify which IPs can send mail on their behalf. Receiving servers check SPF records to verify the sender. Proper SPF configuration improves deliverability and prevents your domain from being used in phishing.
Examplev=spf1 include:_spf.google.com ~all
DomainKeys Identified Mail—an email authentication method that uses cryptographic signatures to verify the sender.
DKIM adds a digital signature to email headers. Receiving servers use the public key published in DNS to verify the signature. This confirms the email wasn't tampered with and actually came from the claimed domain. DKIM improves deliverability.
ExampleDKIM-Signature: v=1; a=rsa-sha256; d=example.com; s=selector;
Domain-based Message Authentication, Reporting & Conformance—a policy framework that builds on SPF and DKIM.
DMARC tells receiving servers what to do if SPF or DKIM checks fail: reject, quarantine (send to spam), or deliver anyway. It also provides reports on email authentication results. DMARC protects your domain from being used in phishing and spoofing.
Examplev=DMARC1; p=reject; rua=mailto:[email protected]
The percentage of sent emails that fail to be delivered to the recipient's inbox.
Hard bounces (mailbox doesn't exist) indicate invalid addresses. Soft bounces (full inbox, temporary server issues) may resolve later. Bounce rates above 2% harm sender reputation. Email validation reduces bounces to under 1% by removing invalid addresses before sending.
ExampleSent 1000 emails, 25 bounced = 2.5% bounce rate
