Notices

I don't know how lame the osso-email notification is, as I've not used it. See the Preferences/Mail Handling/Receiving page for Claws notification options.

I have many imap folders and that makes checking for new mail very slow. It seems that claws issues a status for every folder (this should be pretty fast) and if there are new messages it immediately selects the folder to get the headers. Would it be possible to just do a quick status to update the message count, and to delay the fetching of the headers only when the folder is actually selected by the user?

luca, bring up the folder's context menu, select Properties. On the 'General' page you will find the option 'scan for new mail' - you want to turn this off for folders that you don't want included.

Here's a hint, if you want to turn this off for most of your folders, then select it from the properties of the root folder and use the 'apply to subfolders' checkbox. Then turn it on again for those individual folders that you actually want to be scanned

but will it still do a STATUS and inform me of new mail? (btw, what I proposed is what thunderbird does, I want to know if I have new mail, only I don't want the select and header fetching until I manually enter the folder).

No, it won't.