Trying to stay positive, I think you should use the newsletter popup on something like the 3rd or 4th visit. By that time, users have read some of your material and could form an opinion about subscribing to a newsletter.

From my personal perspective, if you punch me in the nose with a sign-up form the first time I visit, not only am I going to dismiss it without any consideration at all, I am going to be suspicious of the subsequent material you present. Changing the timing of this popup could help you a bunch, I think.