SMTP responses

Code

Enhanced code

Text

Value

250

2.6.0

OK: queued as <message-id>

Email accepted and queued for sending. <message-id> is the message ID.

Code

Enhanced code

Text

Cause

What to do

421

4.3.0

Unexpected error.

Internal service error or unexpected processing error.

Resend later. If the error persists, contact support with RequestID.

451

4.4.2

Timeout waiting for data from client

Email body retrieval timeout expired or the connection was interrupted during data transmission.

Check the network connection and client timeouts, then resend.

452

5.5.3

Maximum limit of <N> recipients reached

Recipient limit per email exceeded.

Split the send into multiple emails with fewer recipients.

454

—

Maximum sending rate exceeded

Sending rate limit (rate limit) exceeded for the cloud.

Reduce sending rate and repeat the request later.

Code

Enhanced code

Text

Cause

What to do

538

5.7.8

Authentication credentials invalid

No login or password provided, or credentials have an invalid signature format or are Base64 encoded.

Check your SMTP username and password.

535

5.7.8

Authentication failed

Credentials verification failed: invalid IAM token, API key, or static key.

Make sure your credentials are up-to-date and correct.

534

5.7.8

Authorization failed

Access permissions validation error.

Repeat your request later. If the error persists, contact support.

534

5.7.8

Not enough permissions

Credentials are correct, but the service account is not authorized to send emails.

Assign the postbox.sender role or higher to the service account.

Code

Enhanced code

Text

Cause

What to do

530

5.7.0

Must issue a STARTTLS command first

Command sent over an unencrypted connection.

Establish a TLS connection (STARTTLS or SMTPS) before authentication and sending.

502

5.7.0

Please authenticate first

The MAIL FROM, RCPT TO, or DATA command executed before successful authentication.

Execute AUTH before you send the email.

Code

Enhanced code

Text

Cause

What to do

550

—

Empty envelope senders not allowed

Authenticated client specifies an empty sender address (MAIL FROM:<>).

Provide a valid sender address.

550

5.4.1

identity not found

Sender address not found.

Make sure the sender address was created in Yandex Cloud Postbox.

550

5.4.1

identity not verified

Sender address not verified.

Complete domain ownership verification.

550

5.4.1

identity is blocked

Sender address blocked.

Contact support to find out the reason for blocking.

550

5.7.1

sender is not allowed

Sender not on allowed list for the address.

Use an allowed sender or add the sender to the allowed list.

Code

Enhanced code

Text

Cause

What to do

550

5.4.5

Daily sending quota exceeded.

Daily sending quota exceeded.

Wait for a quota reset or request an increase.

550

5.5.3

too many recipients (recipient count quota exceeded)

Quota for the number of recipients exceeded.

Reduce the number of recipients or request a quota increase.

552

5.3.4

message is too big (message size quota exceeded)

Message size quota exceeded.

Reduce message size: email body or attachments.

552

5.3.4

Maximum message size exceeded

Message size exceeds the server's technical limit.

Reduce message size.

Code

Enhanced code

Text

Cause

What to do

500

—

Line too long

Command line too long.

Check your SMTP command format and shorten the lines as per the RFC 2822 line length limit.

500

—

validation failed or a specific validation message

Request failed to pass validation.

Correct the email as per the error text.

501

—

Syntax error in parameters or arguments

Failed to parse the address in the MAIL FROM or RCPT TO command, or the address is empty.

Make sure the sender and recipient addresses are correct.