David Buxton at Reliably Broken has written 
a good explanation of the way Apple Mail treats email in POP and IMAP accounts, contrasting it (at the end) with the way Entourage handles each protocol.
As he notes:
Now when you go to remove an IMAP account Mail.app deletes all the local mailboxes for that IMAP account. This is not a problem, after all those local mailboxes are simple caches; the only reason the client keeps a copy is as a performance optimisation (as noted above).
Now when you remove a POP account Mail.app deletes all messages sent or received via that account, even though there will be no copy of those messages on the server (especially true for sent messages).
Not paying attention to this often has tragic results, as you can read in “The Mail POP Disaster: When it’s gone, it’s gone” and in Apple’s Mail Discussions (passim).
David dislikes this behaviour for POP accounts. He concludes: “This is not useful or intuitive – it is a bad design.” And he is not alone, by any means.
What do you think?
Not normally a huge Apple fan-boi, I actually side with the company on this one.
First, Apple gives you a big, fat warning when you attempt to delete a POP account, telling you quite plainly what will happen next — that this action will delete the settings, mailboxes and messages associated with that account:
Secondly, this behaviour makes sense. When you think of “an email account”, do you think of just the settings, or the mailboxes and email in that account as well? When users want to delete an account, Apple is right to take them at their word, and to delete everything.
Or to put it another way, to what extent are companies like Apple obliged to protect users from themselves? Some of my friends in User Support have strong (maximised) views on this, but may not be completely disinterested.
I might be wrong. I am open to persuasion. It just looks to me like Apple is getting panned for designing a process that actually does what the user wants.
Of course, the real moral of the story is not about design. It is backup, backup, backup!
It’s not Apple’s fault that so few people make them. I remember being appalled to learn during the 2006 WWDC Keynote that “only about four percent of users are utilizing automated software for backing up important files — only a quarter of users back up in any way whatsoever on a regular basis.” (Thanks to MacWorld for a transcript of the event)
Since Leopard, there’s no reason (apart from the performance hit and a few small annoyances) why people aren’t running Time Machine. Or one of the many other excellent backup solutions.
Just make sure that you are backing up up all the Mail files you should be.
Tags:
Apple Mail,
backups,
bad design,
imap,
mail.app,
POP,
timemachine
Mail.app users with Hotmail or Yahoo Mail accounts have long had to use third-party plugins to get hold of their emails.
Lion’s mail.app animates its windows. When you open a new message or reply to an existing one, the window “zooms out” to greet you. 
James Dempsey 
Speaking of 
Spotlight searching in Apple Mail is pretty good, but what if it could be even better? 
