your mail server will be retrying your mail

Not quite true. It is in the general case yes, but Net::SMTP handles the connection itself, and does not hand off to your MTA, so it will deliver the mail, or die in the attempt :) (update: oops, unless you connect to your MTA... but if you're connecting directly to their MTA, in the hope of collecting the response code and message, this would be the case).

the remote machine will accept the mail, and then it will send back a bounce

Most notably, aol.com does this. Their user base being the size it is, I assume they decided that it would be too difficult to validate addresses on the perimeter in a timely manner. So they accept it, and then they can take all the time they like to figure out whether it can be delivered. This means that they then have to deal with bogus return paths for bounced spam, but in their terms of use they do say that they will reject mail from your host if a certain percentage of bounces bounce back to them.