Question 1

Does SMTP validation send actual emails?

Accepted Answer

No! SMTP validation simulates email delivery by connecting to the mail server and asking if the mailbox exists, but disconnects before sending any actual message. The recipient never receives anything.

Question 2

Why is SMTP verification more accurate?

Accepted Answer

SMTP directly queries the mail server responsible for the email address. While DNS/MX checks confirm domain configuration, only SMTP can verify a specific mailbox (user account) actually exists on that server.

Question 3

What is greylisting?

Accepted Answer

Greylisting is an anti-spam technique where servers temporarily reject first delivery attempts. Legitimate senders retry; spammers usually don't. A greylisted email is likely valid but requires retry for confirmation.

Question 4

Why do SMTP checks sometimes timeout?

Accepted Answer

SMTP requires connecting on ports 25, 587, or 465. Many cloud providers block these ports to prevent spam. Additionally, mail servers may be slow to respond, rate-limit requests, or have firewalls blocking validation attempts.

Question 5

Can SMTP validation be blocked?

Accepted Answer

Yes. Mail servers can implement rate limiting, IP blocking, or hide mailbox existence for privacy. Gmail and other large providers may limit external verification. Our tool handles these scenarios gracefully.

Question 6

What's a catch-all domain?

Accepted Answer

Catch-all domains accept email to ANY address, even non-existent ones. For example, anything@domain.com accepts mail. This makes SMTP verification unreliable for such domains - we flag them so you're aware.

Question 7

Should I always use SMTP validation?

Accepted Answer

SMTP is most accurate but slower (2-5s per email) and subject to rate limits. Use SMTP for critical emails or small lists. For bulk validation, consider DNS validation first, then SMTP for higher-value addresses.

Question 8

What SMTP ports are used for validation?

Accepted Answer

Our validator attempts port 25 (standard SMTP), port 587 (submission), and port 465 (SMTPS/SSL). We automatically try the best port based on the mail server's configuration and network environment.

Question 9

Can SMTP validation harm my IP reputation?

Accepted Answer

No. Our tool uses established validation protocols and respects server limits. We don't send spam or abuse connections. However, excessive validation from your network could trigger rate limits on some servers.

Question 10

Why do some servers return fake positive results?

Accepted Answer

Some mail servers accept all RCPT TO commands (catch-all) to hide whether mailboxes exist, protecting privacy. Our validator detects catch-all behavior and flags these as 'unknown' rather than 'valid'.

SMTP Validation - Verify Email Deliverability

Why Use SMTP Validation

Highest Accuracy Available

Real-Time Verification

Catch-All Detection

Protect Sender Reputation

SMTP Verification Process

Server Connection

Mailbox Query

Response Analysis

SMTP Validation FAQs

Related Email Validation Tools

Email Verifier

DNS Email Validation

Check MX Records