Hi that tracking url seems uncorrect, have you copied and pasted the complete one? an untrusted url is a tracking url which has not been signed with the Newsletter secret key (only checked for tracking of url pointing outside your domain).
i do love your plugin so much – thanks for this gorgeous work. Regarding tracking I have been facing the same issue Nick did. For the last 9 Newsletters I switched off tracking as it made me mad. Do you know about any solution how to avoid this wrong tracking url?