Error codes returned by ImprovMX’s SMTP servers

Here is a list of error codes returned by our server when you try to send an email. This should help you better understand why an email was refused and if it’s something on our end or yours.

  • 5.9.0 – Loop detected: Email is sent and forwarded from/to We block these messages in order to avoid loops

  • 5.9.1 – Bounces sents from ImprovMX are not really sent and blocked here.

  • 5.9.2 – The domain was not found.

  • 5.9.3 – Our database returned invalid pieces of information about the requested recipient’s domain

  • 5.9.4 – Our anti-spam check failed. We need the sender to retry sending.

  • 5.9.5 – Unable to correctly read the forwarding recipient (where to forward the email to)

Still have questions?

If you have any other queries please get in touch with our support team.

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