---
title: "SMTP dialog errors"
sidebar_label: "SMTP dialog errors"
description: "Possible errors when sending emails via the mail service"
sidebar_position: 2
---

import {CustomTable} from '@selectel/docux/components'
import Formbricks from '@theme/MDXComponents/Formbricks'

# SMTP dialog errors

Selectel mail service uses the SMTP protocol. When sending mail from your server to the service mail node, the following SMTP dialog errors may occur.

<CustomTable>
  <table>
    <tbody>
      <tr>
        <th>`550 bounced check filter`</th><td>The email address of one of the recipients is in the [stop list](/email-service/stoplists.mdx).<br />If more than one recipient is specified in the message, retry sending for each recipient separately. If the address is in a local stop list, you can [find and remove the address from the local stop list](/email-service/stoplists.mdx#find-and-remove-email-from-local-stoplist)</td>
      </tr>

      <tr>
        <th>`501 from domain not trusted`</th><td>The domain from which the mail is being sent has not been added to the list of allowed senders. Ensure that you have correctly [connected the service for the domain](/email-service/connect-email-service.mdx)</td>
      </tr>

      <tr>
        <th>`421 SMTP command timeout — closing connection`</th><td>The server closed the connection because it was inactive for more than 120 seconds. To resolve the error, restart the SMTP dialog</td>
      </tr>

      <tr>
        <th>`450 ratelimit exceeded`</th><td>The rate limit for sending via the resource has been exceeded — 100 emails per five minutes for all resource domains. Wait a few minutes and retry sending</td>
      </tr>
    </tbody>
  </table>
</CustomTable>

<Formbricks />