Many businesses never embark on email campaigns because they feel that marketing emails might be considered as a form of spam. However, those for whom an email campaign is an essential part of marketing, have a definite advantage of the former group, and will gain a greater market share for their product.
What this has meant is that the seller has the perfect chance to build up a relationship with the prospect. This in turn will open up many other chances in future for making sales. This works out much best and much more effectively as an email marketing campaign than the one-off hit or miss effort.
It is better by far to build your own opt-in list, and if you do not yet have one that should be your first step. It will take time, but is necessary for your success, so put your email campaign on the back burner for now and get that list started.
Always make sure to look for incoming messages from subscribers. Doing so will make sure that you are not bothering anyone who does not wish to receive the emails any more and also give you an opportunity to read any feedback that your customers may have.