You could argue that HTML and RTF have no place in email and I’d agree but for where I work it is the only choice.

I don’t disagree. So the archive button, transfers the messages to a different place: On My Mac/Inbox.

I am convinced by those who suggest the addition of another button to the dialog.

Users should be presented with two buttons — “Archive” or “Delete” — and be forced to make a choice in order to progress.

This seems very sensible, now that I think about it!

I really wish there was a better email client for Mac than Mail.app. One that handled IMAP gracefully and whose filter function was able to handle something like “copy message to mailbox A and then move the message to mailbox B”. Or be able to automatically filter other IMAP mailboxes other than inbox for those of us using procmail to do some pre-sorting. Alas, Mail.app is the only thing going other than Thunderbird and Thunderbird has a crap UI.

When you think of “an email account”, do you think of just the settings, or the mailboxes and email in that account as well?

I think this depends entirely on which model you are used to. For users that have only ever had POP accounts, and have never gotten used to the idea that their mail “lives” on the server, I think it really is going to be the former. Their e-mail is on their computer. The account is how they get new mail. Ben is right to mention the “post office” analogy of POP — if you have a PO box, and you shut it down, do you expect Postal Service employees to come into your house and shred your old mail?

This is a recipe for massive and destructive data loss. Yes, users should protect against data loss by backup, but that doesn’t mean Apple should be laying mines for them.