Invariably on logging on to server I get an error message saying that the pop host 3 has terminated your connection. Any ideas how to cure this problem?

Is this the exact error message? What mail client are you using? (Outlook, Windows Live mail, Thunderbird, etc). The Microsoft link below thinks this behavior is due to Microsoft Exchange Server configuration. Are you getting mail from that (I suspect not)?

Error message: Your server has unexpectedly terminated the connection (http://support.microsoft.com/kb/278637)

It could be a firewall problem also. Are you using a firewall? Which one? Do you have a personal firewall installed (like ZoneAlarm or an anti-malware "suite")?

Hello, I am using Outlook. I don't have Firewall, but do use Malwarebytes software along with Avast anti virus. However, the problem is not consistent, as sometimes I can log on OK.

Please post the exact error message. I'm not familiar with Malwarebytes, but if it has a firewall component, it could be that.