Free Email Verification Tool

Verify any email address in seconds. Check deliverability, detect catch-all domains, and identify blacklist status — no signup required.

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Connecting to mail server...

Why Email Verification Matters

Clean email lists protect your sender reputation and ensure your messages reach real recipients.

Reduce Bounce Rate

Remove invalid email addresses before sending to prevent hard bounces that damage your delivery reputation.

Protect Sender Reputation

High bounce rates signal poor list quality to ISPs, reducing inbox placement for all your future campaigns.

Avoid Spam Traps

Detect blacklisted domains and known spam traps that can trigger immediate blocking by major email providers.

Improve Campaign ROI

Focus your budget on verified, reachable recipients instead of wasting sends on addresses that will never engage.

How Email Verification Works

Four technical steps to determine if an email address can receive messages.

DNS MX Record Lookup

Query the domain's Mail Exchange records to identify which servers handle email delivery for that domain.

SMTP RCPT TO Verification

Connect to the recipient's SMTP server and simulate sending a message to check if the server accepts the address.

Catch-All Domain Detection

Identify domains configured to accept mail for any address, which makes individual address verification unreliable.

Blacklist & Risk Analysis

Check if the domain appears on known spam blacklists or exhibits characteristics of disposable email providers.

Challenges in Email Verification

Technical obstacles that make email verification complex and require sophisticated detection methods.

Catch-All Domains

Many organizations configure their mail servers to accept mail for any address at their domain, regardless of whether the mailbox exists. This makes it impossible to verify individual addresses — they all appear valid.

Greylisting & Temporary Errors

Some mail servers temporarily reject connections from unknown senders as an anti-spam measure. This requires retry logic and can delay verification results for legitimate addresses.

ISP Anti-Probe Throttling

Major email providers like Gmail and Outlook monitor for verification attempts and may rate-limit or block connections that appear to be probing their infrastructure.

Integrate in 3 Lines of Code

Verify emails at scale with the uSpeedo Batch Verification API. One call, thousands of results.

# BatchVerifyEmail — up to 10,000 emails per request
curl -X POST "https://api.uspeedo.com/api/v1/email/BatchVerifyEmail" \
  -H "Authorization: Basic $(echo -n 'key:secret' | base64)" \
  -H "Content-Type: application/json" \
  -d '{"Emails": ["xxxx@example.com"]}'
Get API Key →

Frequently Asked Questions

What is email verification?
Email verification is the process of validating whether an email address exists and can receive messages. It connects to the recipient's SMTP server to check if the mailbox is active, without actually sending an email.
Is SMTP Probe free?
Yes, SMTP Probe is completely free to use. No signup or credit card required. You can verify email addresses instantly from any browser.
Does email verification send actual emails?
No, email verification does not send actual emails. It simulates the sending process by connecting to the SMTP server and checking if the server would accept mail for the address, then disconnects before sending any message.
What is a catch-all domain?
A catch-all domain is configured to accept emails to any address at that domain, regardless of whether the specific mailbox exists. This makes it difficult to verify individual addresses, as they all appear valid.
How accurate are the results?
Results are typically accurate for non-catch-all domains. However, catch-all domains always return positive responses, so verification can only confirm they accept all mail. Greylisting and temporary errors may require re-verification.
What's the difference between email verification and email validation?
Email validation checks if an email address is correctly formatted (syntax check). Email verification goes further by connecting to the mail server to confirm the mailbox actually exists and can receive messages.

About SMTP Probe

Built by the uSpeedo email infrastructure team, SMTP Probe is a free tool that gives anyone the power to verify email addresses in real time — the same technology that powers our enterprise-grade email validation API.

Our Mission

Every day, billions of emails bounce because of invalid addresses. We believe email verification should be accessible to everyone. SMTP Probe makes professional-grade verification available instantly from any browser, with no signup required.

Core Technology

SMTP Probe connects directly to recipient mail servers using the SMTP protocol to verify mailbox existence without sending any message. Our verification engine performs DNS MX lookups, SMTP RCPT TO validation, and catch-all domain detection.

Why We Built This

  • Transparency — Open-source verification engine for full auditability.
  • Privacy First — We never store or log verified email addresses.
  • Developer Friendly — Full REST API with batch verification via uSpeedo Console.
  • Always Free — 100 free verifications per day. No credit card required.
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