StopBouncingEmail Verification Service — Stop Bounces Before They Happen
Verify every email address before you send. StopBouncing runs six checks per address — syntax, DNS, SMTP mailbox, disposable detection, catch-all identification, and role account flagging — in seconds. Bulk CSV upload or real-time API.
100 free verifications on signup. No credit card required.
How we verify
Six Checks. One Accurate Result.
Each email address passes through a comprehensive verification pipeline. Every check catches different classes of bad addresses.
Syntax Validation
Checks that the address is correctly formatted — no double dots, spaces, or invalid characters.
DNS & MX Record Check
Verifies the domain exists and has properly configured mail exchange (MX) records.
SMTP Mailbox Verification
Simulates an email delivery handshake to confirm the specific mailbox exists — without sending any message.
Disposable Email Detection
Identifies throwaway addresses from thousands of temporary email providers (Mailinator, Guerrilla Mail, etc.).
Catch-All Domain Detection
Detects domains that accept all email regardless of whether the mailbox exists — never falsely marks these as invalid.
Role Account Detection
Flags shared inboxes like info@, support@, or no-reply@ that typically have low engagement rates.
What Each Result Means
StopBouncing returns four possible statuses — each with a clear recommended action.
The mailbox exists and is accepting messages. Safe to send.
The address does not exist or the domain has no MX records. Remove immediately.
Could not confirm — catch-all domain, SMTP block, or temporary outage. Do not treat as invalid.
Temporary address from a throwaway email service. Usually inactive within hours or days.
Use cases
Who Uses Email Verification
Anyone who sends email or collects email addresses needs verification. Here is how different teams use it.
Email marketing
Verify your list before every campaign. Invalid addresses generate hard bounces that damage your sender reputation with Mailchimp, Klaviyo, and every major ESP. Keep bounce rates below 2% to avoid account suspension.
SaaS & app signups
Block invalid and disposable addresses at registration via the API. Prevent fake accounts, reduce welcome email bounces, and ensure activation emails reach real users.
B2B outreach & sales
Contact databases decay at 20–30% per year as people change jobs. Verify prospect lists before outbound sequences to avoid wasting quota on dead addresses.
E-commerce
Order confirmations and shipping notifications depend on valid addresses. A bounced transactional email frustrates customers and raises your overall bounce rate.
Lead generation
Verify leads immediately after capture — before they enter your CRM or nurture sequence. Stop paying to nurture contacts that were never real.
List reactivation
Re-engaging a dormant list without verifying first is the single most common cause of sudden bounce-rate spikes. Always verify before re-activating contacts who haven't heard from you in 6+ months.
How SMTP Verification Works
SMTP verification simulates the start of an email delivery session without sending any message. Here is exactly what happens for each address checked.
DNS lookup
The verifier queries DNS for the domain's MX records — the mail servers configured to receive email for that domain. No MX records means the domain cannot receive email at all.
TCP connection
The verifier opens a TCP connection to port 25 (SMTP) on the highest-priority MX server. If the server doesn't respond, the address is marked Unknown rather than Invalid.
EHLO handshake
The verifier sends an EHLO command identifying itself. The mail server responds with its capabilities. This is the standard opening of any SMTP session.
MAIL FROM
The verifier sends a MAIL FROM command with a generic sender address. The server acknowledges it. No actual email content is involved at this stage.
RCPT TO
The critical step. The verifier sends RCPT TO with the address being checked. The server responds: 250 OK (mailbox exists), 550 (mailbox does not exist), or 252 (can't verify — catch-all). The connection is then immediately closed.
The entire process takes 1–3 seconds per address. No email is sent, no message is delivered, and your sending reputation is not affected.
Verify in Three Steps
Upload your CSV
Drag and drop your email list in any CSV format. Our parser finds the email column automatically.
We verify every address
StopBouncing runs all six checks concurrently — most lists complete within minutes.
Download clean results
Get a CSV with verification status added. Filter by Valid, Invalid, Unknown, or Disposable and export.
Frequently Asked Questions
What is email verification?
Email verification is the process of confirming whether an email address is valid, deliverable, and safe to contact. It goes beyond simple format checking — it verifies the domain has mail records and the specific mailbox exists on the mail server.
How does SMTP email verification work?
SMTP verification connects to the recipient's mail server and simulates the first stage of email delivery. The verifier opens a TCP connection, exchanges EHLO and MAIL FROM commands, then sends a RCPT TO command with the address being checked. The server responds whether the mailbox exists — without an actual email being sent. The connection is closed immediately after the check.
Will email verification hurt my sender reputation?
No. StopBouncing's verification process uses industry-standard SMTP techniques that do not involve sending real emails. Your sender domain and IP are not involved in the verification process — the verification uses its own infrastructure.
How accurate is email verification?
StopBouncing achieves over 98% accuracy on clearly valid and clearly invalid addresses. Catch-all domains (which accept all incoming mail regardless of the mailbox) are flagged as 'unknown' rather than guessed, keeping our accuracy rate honest. No service can verify individual mailboxes on catch-all domains.
What file formats are supported for bulk verification?
Upload any CSV file with an email column. Our parser automatically detects the email field header — no specific column name is required. Results are available for download immediately after verification completes.
What is the difference between email verification and email validation?
Email validation checks whether an address is correctly formatted (syntax). Email verification goes further: it checks DNS records, MX configuration, and performs an SMTP handshake to confirm the specific mailbox exists. A correctly formatted address can still be completely undeliverable — verification is the only way to know.
How often should I verify my email list?
Verify before every major campaign, and quarterly at minimum for active lists. For lists that haven't been mailed in 6+ months, always verify before sending — email addresses decay at roughly 20–30% per year. B2B lists degrade faster than consumer lists due to higher job turnover.
Learn More
How Email Verification Works
Deep-dive into every check we run.
Bulk Email Verification
Verify thousands of addresses at once.
Email Verification API
Integrate real-time verification into your app.
Disposable Email Checker
Detect and filter throwaway addresses.
Catch-All Email Addresses
Understand what catch-all means and how to handle it.
Reduce Your Bounce Rate
Practical strategies to improve deliverability.
Start Verifying Today
100 free verifications on signup. Pay-as-you-go credits from €0.0006 per email. No subscription required.