Skilled Technician for Email Fix

We need a skilled technician to resolve our corporate email issue. Currently, we can only send emails internally within our domain and cannot send emails to external addresses. We were told that our website's email system is the root cause. We are looking for someone who can diagnose the issue, identify the problem, and implement a solution so we can send emails to external addresses without any issues. In addition we were told by our host that our website (same domains) were hacked and the criminals used it for mass email blasts, in 100s of thousands. We are also looking to implement a system that will prevent this in the future. We will work with the right candidate on this, suggest pricing.