SMTP enhanced status code 5.7.0

What the registry says

The basic codes it travels with

• 220 <domain> Service ready
• 450 Requested mail action not taken: mailbox unavailable (e.g., mailbox busy or temporarily blocked for policy reasons)
• 454 Temporary authentication failure
• 500 Syntax error, command unrecognized
• 501 Syntax error in parameters or arguments
• 503 Bad sequence of commands
• 504 Command parameter not implemented
• 530 Authentication required
• 535 Authentication credentials invalid
• 550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)

In practice

X.7.0 is the code providers reach for when the reason is security or policy and they do not use a more specific code. Gmail uses 421 4.7.0 for a missing PTR record, TLS required by the recipient domain, an IP not on an allowlist, and low IP or domain reputation, and 530 5.7.0 to require authentication or STARTTLS. The number alone will not tell you which; the text will.

What the sender should do

Read the text after the code, which carries the real reason. Then check authentication, TLS and your sending reputation, in that order.

How providers use X.7.0

Quoted from each provider’s own error reference.

• Gmail 421 4.7.0

  Connection expired, try reconnecting. For more information, go to About SMTP error messages.

• Gmail 454 4.7.0

  Too many sign-in attempts, try again later. For details, go to SMTP relay service error messages.

• Gmail 552 5.7.0

  This message was blocked because its content presents a potential security issue. To review our message content and attachment content guidelines, go to File types blocked in Gmail.

• Gmail 503 5.7.0

  No identity changes permitted. For more information, go to About SMTP error messages.

• Gmail 550 5.7.0

  Email relay denied ip-address. Invalid credentials for relay for one of the domains in: domain-name (as obtained from HELO and (E)MAIL FROM). Email is being sent from a domain or IP address which isn't registered in your Workspace account. Please login to your Workspace account and verify that your sending device IP address has been registered within the Workspace SMTP Relay Settings. For more information, go to SMTP relay service error messages.

• Gmail 554 5.7.0

  Too many unauthenticated commands. For more information, go to About SMTP error messages.

• Gmail 530 5.7.0

  Authentication required. For more information, go to Can't sign in to your Google Account.

Common questions

What does 5.7.0 mean?

X.7.0 says a security or policy reason caused the failure, without naming it. Providers use it widely: Gmail sends 421 4.7.0 for reputation and TLS deferrals, and 530 5.7.0 for authentication required.

What is the difference between 5.7.0 and 2.7.0 and 4.7.0?

They share the subject and detail digits, so they report the same condition, "Other or undefined security status". The first digit is the class: 2.x.x success; 4.x.x persistent transient failure: retrying later may succeed; 5.x.x permanent failure: resending unchanged will not succeed.

What should I do about 5.7.0?

Read the text after the code, which carries the real reason. Then check authentication, TLS and your sending reputation, in that order.

Would an email verifier have caught 5.7.0?

Partly. The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.

Full guides for this code

• 421 4.7.0 — temporarily deferred, try again later
• 530 5.7.0 — must issue STARTTLS or authenticate first
• 552 5.7.0 — Blocked for a security risk in the content (Gmail)
• Yahoo TSS04 — Yahoo temporary deferral