Fix email issue in cpanel

We have had an issue with emails on our new dedicated server. Employed someone on here to fix, the problem was okay for a short while but has come back. He did a temporary fix routing the emails via another server but now not working again and he wont reply to any emails, hence he wont be getting any further work. I believe the issue is something to do with permissions but not too technical so that is all I can advise. The issue seems to be with just one domain on the server. I will be away from the office for the next 30 mins and then will select winning bidder. Also need the work starting straightaway really so no point bidding if this is an issue. Thanks