I have a very large collection of emails on my server (it is my life). I just want Thunderbird to download to my local hard drive emails I ask for. I have unsync'ed the vast majority of my folders. I have compacted all folders. But I can not get rid of the emails Thunderbird has already downloaded to my local hard drive. These are filling all my storage space. Before I go buy a bigger computer, how do I get rid of them?

Note, I don't want to get rid of them on my server. I just want Thunderbird to go get the ones I ask for - and to get rid of the legacy of synching past.