So many companies send emails with multiple different address. For example, Citibank could send from citicards@info6.citi.com or CustomerService@thankyou.citi.com. Bank of America can be communications@servicing.bankofamerica.com or onlinebanking@ealerts.bankofamerica.com. If the "Citibank inbox" just takes the first address that Citi happens to use and auto rejects all future others, user will lose critical emails without even knowing. There is no way either user or the app could guarantee an entity will ever only use one address for legitimate reason.