Error: NDR - Authentication Credential Invalid (Exclaimer Cloud – Signatures for G-Suite)


You are using Exclaimer Cloud – Signatures for G-Suite, and start to receive bounce-backs from sent messages, stating:

535 5.7.8 Authentication credentials invalid [Response from was 534 5.7.14 q6sm95039edh.25 - gsmtp] (e2b5e025-d561-4261-b5ac-e47a87b7179d,92611451-15de-4cbf-ba58-879f67066cc6)


This issue is caused by the SMTP authentication failing, when your messages attempt to proxy through our service back to G-Suite.


This most common cause of this issue is that the user account used for the SMTP authentication process has an expired password or the authentication attempts are being rejected due to throttling.

As the service also utilises IP based authentication as well, we can now remove the SMTP credentials to resolve these issues without affecting the use of our service or your mail flow.

To do this, please follow the steps below:

Remove SMTP credentials from your tenant

  1. Login to Exclaimer Cloud here.
  2. Launch your subscription:

  3. Click the ‘Hamburger’ icon in the top right and go to Settings:

  4. Select the Mail Flow tab, then click Edit:

  5. At the next screen, select the I have completed the setup in G Suite option and click Save

    This will remove the previously saved credentials from the service and revert to the IP based authentication method.


Note: If you wish to continue to use SMTP authentication, speak to our support team via the following link

Haven't found a solution to your problem?

Please click the button below, login to the Exclaimer Cloud portal and raise a support ticket. A member of the Exclaimer Support team will then be in touch.

Raise a support ticket