User Names or Email for User Accounts

Can we please have the option of a user name OR email address for user logins.

I have membership database with 2000 members, some (400) members have no email address and some members use the same email address as their husband, wife or partner. Some of the junior members use their parents email. This stops me giving them their own account as the email field is required and I need a way for them to login.

I have to produce fake email addresses just for the purpose of login which really isn’t ideal.