Can't receive emails on Domain name

Advert test
I'm have a problem with a domain that I recently moved to Blacknight sheared hosting.

I moved the domain name last week but the company can't receive there emails. They can send them out but they can't get them in.

I have checked the IP's are correct and that everything else is working. All appears to be fine!!!

I have put a support question in about the problem this morning but as of now I still have no reply or solution to this problem. The client currently has no emails coming in and I want to get them sorted by tomorrow.

Can anyone help with this please.