Why could mail agents stop working?

Question

Windows

Since the beginning of the week, agents have gradually stopped working in one domain zone, out of 6 computers, only 1 can now enter the agent.
At first I thought someone closed the MB port 443, but then why does 1 computer work?
Where and what to watch on Windows Server 2008

Answer 1

And what exactly does not work, what error does it write? What server do the agents work with? Maybe the problem is in dns, but in one computer it's just static or something else is written. Details, details needed.