Nextcloud vm fails to start postfix mail transport

Hi all…

A new problem has befallen me after a smooth install and use of about a week with my Nextcloud VM. Today I could not get access to my NC instance using my domain name. However if I try with the local ip it’s fine. When I restart the VM, during boot up, as the services are starting one has a fail: FAIL: to start postfix mail transport agent (instance -)

Now I’m stuck… If I try to recover from a back up that I have from three days ago of the instance I still get the same error…

Any ideas please anyone???

Many thanks