That's odd. For me bounced messages are returned to me before I even exit the mail app. Seriously, it's that fast. Maybe it's Softbank's servers here in Japan that are really fast.
But the problem is if the smtp server is not contactable.
You wont get a bounced message at all.
The message just sits in the outbox.
Your swoosh has already happened, so you are none the wiser until your colleague says, where's that email you said you were going to send.
Terrible.
.