I have a very big multisite. And I got a request to enable option that multiple users can use the same email. I found a plugin "Allow Multiple Accounts" which doesn't work properly. I should figure out some other solution for that. I know that I could use something like adding +sometext to every email, so it will show different to Wordpress. Do you have some other solution, that can be done here?
You can use
UPDATE: for a non Multi-site setup try this code: