If one of your customers has multiple enterprises, then a different OkiOki account must be created for each enterprise of that customer. Today you can only create one account per email address. This means that today you need a unique email address for each OkiOki account, and you cannot use one email address for multiple OkiOki accounts.
So basically, the customer should have a separate email address for each enterprise. If the customer does not have separate email addresses, but uses a Gmail or Outlook address for the correspondence of their enterprises, there is a possible solution for this.
Gmail and Outlook offer task-specific email addresses, which you can create by adding a plus sign. In this way, all your messages still end up in the same mailbox, but you have different email addresses that you can use for other purposes.