Some years ago, in my pre-Linux days, I used an email client which did most, but not all, of what KMail does.
It had one handy feature which I haven't found any way to replicate in KMail, and I'm wondering if anyone can suggest any way of doing it - or whether I should file a bug requesting it as a new feature!
The feature (at its simplest) was this: if I had mail in my inbox, and replied to it, the original mail was transferred to a 'filed' folder. This could be fully automatic (unprompted) or prompted (hit the 'send' button on a reply and a 'file the original mail - yes/no' box came up), or the filing behaviour could be turned off completely. It was useful because it prevented my inbox filling up with dealt-with mail until I got round to manually filing it away!
That software only supported one 'filed mail' location and one behaviour setting - personally I think the ideal would be for the behaviour to be configurable per-folder, ad with the filed location also configurable per-folder.
Am I missing an existing way of doing this, perhaps through some use of filters I've missed, or would this be something new?