Email Address Customer

I have a costomer with various entities and would therefore like to link his email address to the various different entities, but the Akauting system shows that "this email is already used".
What is the alternative? Or any suggestions?

When you say entities you meant companies on akaunting or Customers?

Yes. I have Customers that have different businesses, which I created as different Customers, but they all have the same email address. How do I get past this problem?

My company provides IT support to hotels and some properties (customers) have the same management team. We are also looking to have a way that one email address can be assigned to multiple customers. Please implement.