I'm trying to make a system where the sign up would be allowed or denied based on the domain of the mail.
So let's suppose that only people from
company.com are allowed to sign up on that system.
Let's pretend that the system admin from
company.com has total control of all mail addresses that are created.
My question is, is there any security issue that would allow someone that does not belong to that company to get sign up on the system?
Would an attack as DNS poisoning affect this system making mails to be redirected to another domains?