Unsubscribes and opt-outs are common to any Email Marketing Campaign and so, you must try to look into the issue and identify the reason for the problem. Generally, too many emails or irrelevant emails that may over-stuff the recipient’s inbox cause the most inconveniences. In the worst case, the recipient’s do not remember the subscription and opt out even in the initial stage. So, it's better to be picky with the design and style of your emails. Sharing  personalized emails with amazing offers, discounts and rewards will make them stay or atleast give a try to your services. There are many more reasons to avoid unsubscribing, but their effective implementation is possible only when you realize the exact problem.