You may want to try using a URL shortener like goog.le. I know it's another system to keep track of data in, but if it's a text email, then the end user isn't downloading the information needed to track activity within the email (at least, to my understanding).
I've done this in the past, however, and sometimes the link breaks. But if it's a text email anyway, they're most likely going to need to copy+paste the URL no matter what.