thank you for your answer. We have thought that the sql express edition is free to use regardless of the hardware it is installed on. But the microsoft man stated that the express edition is only free to use when it is installed on a server which has only one cpu and a maximum of 4 cores. I just performed a search on the internet and didn't find anything which approves the statement of microsoft.
We have installed Veeam Endpoint on a two socket machine with 6 cores per cpu and therefore we have to buy the sql standard edition. I think he mixed this with the maximum specs of the cpu the express edition is able to use.