What to do if one doesn't want to receive email bounces?

Using option #1 is always the better solution. Think of it like paper mail; a functioning return address is mandatory. Email is only getting more restricted (DMARC, etc) due to spamers taking advantage of the open policy. It's really not that hard to automate dealing with replys you don't care about. But likely less than 10% of email servers are that restrictive so you can probaby get away with it. Also be sure to avoid getting your server listed in a dnsbl.

The rules are lax most places (I can send an email that looks like it's from you which would invoke a sort of DDOS if I sent it to everyone and crafted it to bounce) Look at all the restrictions in Postfix if you want to know what rules might be in effect.

You can't have it both ways; do it properly (#1) or resign to being tagged spammer (by at least some). Google uses [email protected] and that won't ever reach me because my mail server requires a verified sender. Google is the best at anti spam if they can't have it both ways I'm sure we can't.

4 - handle the bounce.

Generally the best approach is to cause the bounce to go to some sort of bounce-handling process so that persistently bouncing recipient address can ultimately be pruned out of your database. Which could be a .forward for "alice", or adjusting the envelope sender to be a handler process.

Whether or not "alice" cares whether the email bounces, the recipient server administrators or filters often do. In many cases, recipient servers count every bounce as negative reputation points. Do it enough, and you end up on their blacklists and you won't be able to get anything through.

Don't chew up other people's resources because you're too lazy to handle it yourself.

In general, I agree that #1 is probably the best solution, you can just discard any returns at the server. Install a .forward that sends messages to /dev/null. It's unlikely your bandwidth bill will hurt.

To the wider discussion as to whether you should care about messages not being delivered, I don't really know anyone processing their own returns at any scale, but services like SendGrid, MailGun, etc.. are great at this, they allow you to send via HTTP POST, they manage reputation for the IP space, and tell you about returned mail and complaints.

For your case that may not be key, but in general, I try to avoid managing my own mail delivery in production these days. So much can go wrong, and it can be such a huge distraction from other aspects of maintaining a large web stack.