The ability to sending email is based on the mail server and the “clean-ness” of your list and not so much our software. If you get a lot of bounces or you get a lot of complaints there is nothing to stop one of the blacklisting systems from blocking you out. It definitely takes daily attention to check blacklisting and respond to ISPs that are having problem with email. One of the pluses with using an emailing service instead of your own mail server is they do the blacklisting work for you because they need to keep their reputation too. The one we like right now is mailgun.net which give you 10,000 FREE emails per month and then the cost of more is very reasonable for higher numbers. In my experience, companies burn a lot more time/money that then realize dealing with just one problem a month.