They don't always make double opt - in email introductions, as it would simply take up too much of their time. (entrepreneur.com)
However, email introduction letters are shorter than regular cover letters and need to incorporate a sum of all that you want to say. (coverlettersandresume.com)
If he or she had sent you a short email introduction and you are ready to respond then make it short as well. (trusteddatingsiteadvisory.com)