The service I work on emails users(B) after their email address has been input by another user(A) of our service. This would allow us to check that the email is

The service I work on emails users(B) after their email address has been input by another user(A) of our service. This would allow us to check that the email is reachable before we attempt to send the email. If it is not we can ask user(A) to check before they proceed.