It is my understanding that all users now have to have an email address, as this will be their username. I completely understand this logic

However, some of the purchasing agents who purchase our products (we're B2B) may not have an email individually for themselves (it may be shared email such as purchasing@clevelandclinic.com) and within that department, there may be several people procurring from our company.
My question: is there a way that we can maintain the 5.x way of logging in for customers that need that functionality? Is this something that can be customized?
Thanks in advance,
Margie