Afrihost Email Server

We have been with Afrihost for a year now, with the same issue every month. We currently have 50 email addresses sending from all over the Eastern Cape. Certain sent emails are never received by the recipient, there is no "bounce back" email to advise us of the problem. Its only when a critical email isnt delivered that we become aware of the problem. We contact Afrihost and have re-explain every time that the problem is their side, and eventually they sort it out which take 24 to 48 hours. Apparently they have public IP addresses which get blocked and then emails get blocked as well.