When a message has a Do Not Send routing policy applied to it, the message is routed back through ZixGateway as though it had been sent with the Send delivery method. If you have different branding for the Encrypt & Send delivery method and the Send delivery method, that message could be sent to the recipients with the Send branding. This is probably not what the recipients are expecting. To preserve the Encrypt & Send branding, include the original message (using the Original or As Attachment options) in the message sent to the recipients.