Note: If you are not the system administrator for the mail servers affected, we encourage you to contact the administrator, so they can look into the issue further.

This error message indicates that your email wasn't accepted because it failed authentication checks against your sending domain's DomainKeys or DKIM policy. DomainKeys and its successor, DKIM, are email authentication technologies, which ensure emails really come from their claimed domain.

We only reject emails for failing DomainKeys or DKIM authentication when both of these conditions apply:

1. The signing domain (i.e., as identified in the "d=" tag of the DomainKeys/DKIM signature) has given us explicit indication that all emails from the domain must be signed and authenticated with DomainKeys and/or DKIM to prevent forgery.
2. The rejected email couldn't be authenticated against the sending domain's policy (e.g., due to a missing or bad signature).

We recommend that you contact your domain's mail administrator and make them aware of the problem.

For more information, please visit DomainKeys and DKIM.