Several clients have complained about their site being blacklisted and unable to send emails to certain clients. We regularly check that our servers are not blacklisted in any way, and will continue to monitor our servers to ensure they are not blacklisted.
Not being on a blacklist, if your email is still being blocked, ask the recipient to add you to his/her whitelist.
More reading from the industry can be found HERE (you can also test your local IP if you know it). You can see if your local computer is blocked HERE and you can also obtain your own IP address.