SMTP Code 252: Cannot Verify User

Success Low severity Address RFC 5321

What it means

SMTP Code 252 means “Cannot Verify User.” The server cannot verify whether the recipient address is valid but will attempt delivery anyway. This is a security measure to prevent address harvesting by spammers.

At a glance

Code252

Bounce typeNot a bounce

SeverityLow

CategoryAddress

What to doNone; the delivery step succeeded

StandardRFC 5321

What it looks like in your mail logs

252 2.1.5 Cannot VRFY user, but will accept message and attempt delivery

What does 252 mean?

SMTP code 252 is returned when the receiving server cannot confirm whether a recipient email address exists, but it will accept the message and attempt delivery. Many modern mail servers respond with 252 instead of definitively confirming or denying addresses during the RCPT TO phase as an anti-spam measure to prevent address harvesting.

This is actually a good security practice by the receiving server. By neither confirming nor denying the existence of mailboxes, the server prevents spammers from probing for valid addresses. Gmail, Microsoft, and most major providers use this approach. You should not treat 252 as an error - your message will still be delivered if the address is valid, and you will receive a bounce notification (NDR) later if it is not.

How 252 plays out

Your server connects and sends a command

The recipient responds 252: the step succeeded

The SMTP conversation continues toward delivery

Common causes of 252

Server deliberately does not verify recipients during SMTP session (anti-harvesting)
Recipient verification is deferred to a later stage of processing
Server accepts all addresses at SMTP time and validates during delivery

How to fix 252

No fix needed - this is normal behavior for most modern mail servers
Ensure your email list contains verified addresses to avoid later bounces
Use double opt-in to confirm addresses before adding them to your list

Frequently asked questions

What does SMTP 252 "Cannot VRFY user" mean?

SMTP 252 means the server cannot verify whether the recipient's email address exists, but it will accept and attempt to deliver the message anyway. This is a positive response; about 95% of the time, the email will be delivered successfully. The server deliberately refuses verification as a security measure to prevent email harvesting attacks through the VRFY command.

Will my email be delivered if I get SMTP 252?

In most cases, yes. SMTP 252 is generally a positive response indicating the server accepted your message despite being unable to confirm the address exists. However, the email may still bounce later if the address turns out to be invalid. If you consistently receive 252 responses followed by bounces, verify the recipient's email address through an alternative contact method.

Why do mail servers return 252 instead of confirming the address?

Mail servers return 252 as a deliberate security measure to prevent email address enumeration attacks. If a server confirmed or denied every address via the VRFY command, spammers could systematically discover valid email addresses. By responding with 252 ("cannot verify but will try"), the server protects its users' privacy while still accepting legitimate mail.

Related bounce codes

Sources & further reading

RFC 5321 · The standard that defines this reply code RFC 5321 section 3.5.3 · Meaning of VRFY and EXPN replies, including 252 when a server will not verify

Reviewed by Jennifer Jackson, Email Deliverability Analyst · June 2026 ← All bounce codes