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Errors in SMTP dialog
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Errors in SMTP dialog

The Selectel email service uses the SMTP protocol. The following SMTP dialog errors may occur when sending mail from your server to the service's mail host.

550 bounced check filterThe email address of one of the recipients is on the stop list.
If more than one recipient is listed in the email, repeat the mailing for each recipient separately to determine which address is on the stop list. If you think that an address was added to the stop list by mistake, remove it from the stop list using the API method
501 from domain not trustedThe domain from which the email is being sent has not been added to the list of allowed domains. To resolve the error, create a ticket
421 SMTP command timeout - closing connectionThe server closed the connection because it was not used for more than 120 seconds. To resolve the error, start the SMTP dialog again

Stop list

The recipient's email address goes into your local stop list if one of the previous sends to it received status:

  • unsubscribe — the recipient has unsubscribed from the mailing list;
  • fbl — the recipient complained about spam;
  • failed — the email address could not be sent to.

Emails to email addresses from the stop list are not sent, the SMTP dialog returns the error 550 bounced check filter.

If you have specified multiple recipients in an email and at least one of the email addresses is on the stop list, the email will not be sent to any of them. To determine which address is on the stop list, send the email separately to each of the recipients.

If you believe an address has been placed on the stop list by mistake, you can remove it from the stop list using API method.