Annoying, perhaps. But reporting it as 'spam' to your mail provider is treating it the same as the bulk nigerian prince scams and v14gr4 p1ll5 junk. It's not.
Sure it is. Just being in possession of someone's email address is not the same as having permission to send to that address.
Confirm the address, and make sure you have permission[1] to send to that address, before sending to an address otherwise your email is exactly the same as 419 scam and goji berry email.
[1] Either from a checkbox where the user has opted in or a pre-existing business relationship. And that's not "I gave you my email address to download your app".
