Following provisioning of Content Encryption, messages delivered via the Content Encryption action are bounced with a terminal rejection by the configured content encryption host.
553-you are trying to use me [server-11.tower-51.messagelabs
553-.com] as a relay, but I have not been configured to let
553-you [18.104.22.168, mail.domain.com] do this.
553-Please visit www.messagelabs.com/support for more
553-details about this error message and instructions to
553 resolve this issue. (#5.7.1)