[b112]

They're referring to the bounced notification message, not the fact that the mail bounced. Verb and noun.

A 5xx is a bounce, and results in a bounced email message. Variances always abound, but I'll stick with my 30 year old terminology, and it is correct.

[jeffbee]

That's fair with regards to your statement, but "doubled112" assigned the agency to Microsoft, saying that "Microsoft bounces" their traffic, which is demonstrably not what is happening.

[b112]

It is what's happening, as I've described. A 5xx is a bounce.

You don't agree with my terminology, but we're not disagreeing on what's happening. In this case, as per my dictionary, 'rejected' and 'bounced' are synonyms. If this was me, and my MTA hitting this Microsoft server, my MTA/server would see the bounce(5xx), then my MTA/server would generate a bounce message(email) which I'd receive in my inbox.

The bounce message is a result of the bounce. The action/cause is the bounce/reject 5xx.

How can you have a bounce message, without a bounce happening?

Again, you don't agree with this terminology, and that's fine. But I'm not pulling this out of a random hat, it's 30+ year old terminology that I've used with endless people locally and online. That doesn't mean your view is wrong, we may just be running into local variances in lingo.

There are all sorts of edge cases in our compute discourse. I ran into a company where they didn't use initialisms to discuss daemons/protocols, but treated them as acronyms. Of course, they didn't really discuss such things often. So when discussing smtp, they'd pronounce it 'sim-tee'. Of course, sntpd, smtpd, snmpd, and others are all pronunced 'sim-tee', which makes for a fun meeting. Think of it as 'I am groot' taken too far. For prudence, I kept enforcing initialisms, which of course resolved this.

Anyhow! Point is, well.. not really sure except info.