The system works after a server restart but then ceases again.
Checked all certificates and disk space etc. so am assuming it is update related as all the effected systems are running on Windows 2008 R2
I have removed 2018-07 cumulative security updates and 2018-07 security monthly quality rollup for Windows Server 2008 R2 to see if that fixes the issue.
It may also be KB4284826 which was installed this morning.
Data Recovery Berkshire
This machine also has the DKIM signing tool installed.
I removed these from an Exchange 2007 WIndows Server 2008 R2 box yesterday and it was still receiving mail this morning.
The systems are still receiving email as hoped following removal of the 12/7/18 and 13/7/18 updates and we have disabled the updates for the time being.
If subsequent updates appear than we shall test if email is unaffcetd on the latest build but with the updates currently only really for new .NET software, we feel that the 2008 R2 boxes are subsequently patched and can be regarded as safe considering they do not browse the internet etc.