When I was growing up my wise mother used to often say “haste makes waste” And then there were other aphorisms with similar sentiment: “patience is a virtue”, ”nothing good happens overnight” etc.
What I’m getting at is that growing a good, responsive email customer list takes time and creativity. I have had a few clients complain that the growth process was too slow. This might have been my fault: my enthusiasm probably caused me to gloss over the time aspect of the process. So I’m saying it now just to be clear: it takes time. But so what. Even if you add five customers a week in a year you will have quite a substantial list. You will have added a lucrative asset to your business for very low cost.