If your hosting account does not have a correct Reverse DNS entry some receiving email servers may reject your email because of this. It is something generic which some mail servers to check for. You can sort this properly a couple of ways…
Update the Reverse DNS for that IP to match the A record you created earlier or if ask your hosting company to do it.
Ask your ISP or hosting company if you can forward your outbound email to one of their mail servers..called a relay server.
You should also make an SPF record for your domain. Read more here: http://www.openspf.org/