Certainly, you have to build your opt-in mailing list. The truth is that it must grow or it will die. That is definitely how email marketing function. The customers that bought from you once may as well buy from you again and maybe they will purchase a lot more times but then they certainly will not re-purchase those products they already bought. For you to sell your first product once more, you really must inject new blood on your mailing list.
There are different tactics to grow your email list. You can even build your list by making it self-propagating. This can be made possible by using viral marketing techniques like including jokes, free of charge …