Having configured Exclaimer Cloud emails are not delivered and an error is reported


Having configured Exclaimer Cloud for the first time (or having changed Mail Flow settings), you see one of the following errors when sending an email:

smtp.eu1.exclaimer.net gave this error: Command refused due to lack of security
Remote Server returned '554 5.7.5 Command refused due to lack of security'


Remote certificate was not validated. Reason: The remote certificate is invalid according to the validation procedure.


550 5.0.350 Remote server returned an error -> 553 sorry, relay of mail is not allowed.


These errors occur when:

  • The MX record for the specified domain (specified during the initial configuration) points to a third party server


  • When you have chosen incorrect settings within the Exclaimer Mail Flow

As a result, emails are not routed back to Office 365 after they are processed by Exclaimer Cloud.


To resolve this issue, you should update Mail Flow settings and specify your .onmicrosoft.com domain. This ensures that all emails routed through the Exclaimer Cloud service will be returned to your Office 365 tenancy, for transmission to the final recipients.

To update Mail Flow settings, follow the steps below:

  1. Log into the Exclaimer portal (exclaimer.com).
  2. Click the Launch
  3. Click the Settings button at the top of the page.
  4. Access the Mail Flow
  5. Under the Mail Routing heading, click the Edit button:

    Mail routing in Signatures for Office 365.

  6. Choose the Static Domain mail routing mode.
  7. Enter your .onmicrosoft.com domain name:

    Enter your.onmicrosoft.com domain name.

    Note: If you are not sure what your Office 365 tenancy domain name is, click here to learn how to find it.

Finding your Office 365 tenancy domain name

If you are not sure what your Office 365 tenancy domain name (i.e. your domain.onmicrosoft.com) is called, you can find it via the Office 365 Admin Center, as follows:

  1. Log into the Office 365 portal.
  2. Open the Exchange Online Admin Center.
  3. Go to Mail flow, and select Accepted Domains.

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