I love that it's easy for my clients because they can just send me their list of emails addresses from people who have already purchased products or services online previously through an affiliate program like Amazon Associates Account / Ebates account etc..
The best thing about this service compared to other similar ones out there is its price as well! It doesn't cost much but we do get charged if you cancel your subscription before 14 days which makes sense since after all it’s not free so make sure what exactly are you getting yourself into first time around!! Also don't forget to check how many email accounts will be allowed per month when signing up otherwise some sites may limit number depending upon where you live/work.