For an overwhelming majority of nontechnical users, no, it is not a good error message. It is filled with confusing technical things that he/she shouldn't have to care about, like HTTP status codes and IP addresses. Even if these people chose to read the whole thing, they still would have no idea what is going on. So it's a terrible error message.
Yeah, but UIs aren't there for reading; they're for using. If I get an undeliverable because the recipient was bad, then the UI just needs to indicate, "Bad Recipient."
People are doing energy management all the time, and that's not a bad thing. They see something that looks technical at a glance (it's got numbers and slashes and run-on sentences) and that's it. They know they're not technical, and they don't aspire to be technical, so they don't waste energy trying to comprehend the message.
I know plenty of non technical people and they all understand the concept of bounced emails. Error 238B is terrible but "can't deliver email to ben.cornwalll@test.com" and 90% of people can understand they miss spelled the guys email address. It's only after that they their eyes gloss over and their mind shuts down.
It would be reasonable to someone reading HN, since we probably are not scared off by technical jargon. Even if the instructions were spelled out completely, the plain-text formatting and numbers (IP addresses) immediately tell the average user that this is over their head and they ignore it. It's not user-friendly for real-world users.
Those would be SMTP codes. I don't see why it's hard not to understand that "your message was not delivered to this user". The traceback should probably be sent to the postmaster rather than back to the user, but that's an anachronism of the mail servers, which were built back in a time when all email users were technical.
