IMAP and Mac Mail client (3.1 under Leopard)

[#1]

OK a problem I've posted about before, when I first started with PlusNet, but STOL haven'tbeen able to solve.
I use IMAP for my PlusNet mail.
I access it via my Mac using Apple's Mail client, and via my iPhone. The inbox works perfectly with both clients, but anything else (sent, drafts) is only visible on my iPhone. My desktop comes up with messages like folder does not exist, whenever I try, even though they are visible in the Mac's Mail client.
I can access it fine via my iPhone, and if I choose, via webmail. But get this, the only messages in the sent folder are ones I sent from the phone, messages I send from the Mac mail client dissapear into the eather (though they do get sent)
So and Max users out there who can tell me what's going wrong?

[#2]

Have you specified each folder's 'job' in Mail? When you add a PlusNet IMAP account in Mail, it'll show you the various folders - Sent, Drafts, Junk etc. - but it won't actually know to use those folders for their respective functions. To make it do this, you need to select each folder in turn, then go to the 'Mailbox' -> 'Use This Mailbox For' menu item, and select the folder's function from the options available.

[#3]

Thank you. No I hadn't done that. I did, and they shifted about in my folders list and gained new icons ...
But, when I try to look in them, I get a dialogue that says:
Unable to open “Sent”
The IMAP command “EXAMINE” failed with server error: Mailbox does not exist, or must be subscribed to.."

[#4]

This  is one of those useless posts where someone says it works for me but I thought I'd chip in just in case.
Your question prompted me to set up my own Mail more systematically - I'd not gone through each mailbox on turn as already suggested.
This is what I did ( in order) in case it gives you any clues
1. Select each mailbox. Use the Message/Use This Mailbox For ... menu to 'assign' it a function. Usually Sent for sent messages etc etc.

2. Open Mail Preferences on your desktop machine.
For each account select 'Mailbox behaviours' and check the required behaviour. Sounds like you want most of your stuff to remain on the  server so you can see it from anywhere.
I tested it by sending a message from my iPhone. It promptly appeared in the Sent folder and was viewable from my iMac. And then vice-versa which also worked.

[#5]

Thanks for your thoughts, but no, it doesn't work for me. I've been trawling the Apple forums, and it looks to be a common issue with Mail under Leopard. So I've added my rant to the forums and I think its up to Apple to sort.
Meanwhile, I've moved to Thunderbird, which does it all perfectly (as does Entourage even!). Pity really as I liked Mail's system level integration with Address Book and data detectors.