This same process also works for Smart Attachments.
If you would like to enable PoliteMail tracking on a message, but would like certain links to NOT be tracked, simply add ?notrack=true to the end of the URL.
After you’ve inserted your links into your email, right-click on the hyperlink and choose Edit Hyperlink.
Now add ?notrack=true to the end of the URL in the Address field.
When you look at the results, you will see that the PoliteMail link has been tracked, but the Google link has not.