realsparticle wrote:I have just shutdown the server and put it back to 4 CPU and 8 GB all starts fine and the server is back up and running and responsive.
This makes no sense!
In my more than ten years dealing with Zimbra, my experience has been that most issues like yours are DNS or configuration related. Happy to help but we need specifics.
If it's working fine for you now and it stays that way, great. If you made no changes at the OS level then it speaks to an issue at the hypervisor level or lower, not at the OS/Zimbra level.