Bounce email handling

I am not sure how can you that but we are sending to many emails unreal email addresses. This is because of expired email, retired, turned to be offline for some reason.
 
So I can't get users real email and code is still trying to send email. I am afraid of this could be handled as a spam or flood.
 
This could be useful when a forum admin starts a brand new domain with instant login without email confirmation pending. After abuse users he can change way to confirmed email address.  But he can't be sure which one is real which one is not real.
 
Also for the email to user function is can get benefit from this. Think a user send a big email from the forum. But it never reaches. And he never knows it haven't reach.
 
A mod sends a email also after moving or deleting a user post. And writes explanation this is also this can't be reach to the user. Email list building will benefit it too. Which one is real which one is not.