Its true. By default Icedove (that’s Thunderbird to non-Debianists) puts the newest emails at the bottom of the message list. This is wrong and evil (I may be exaggerating). It took me a while to find the proper solution and then a bit longer to figure out I needed to delete the .msf files from my ~/.icedove/123xyz.default/ folder to stop the old sort order from staying put. And then a bit longer again to have the correct email be selected after I deleted one. You probably want to back up your profile before trying this.

1. First we open Edit | Prefs | Advanced | General | Config Editor . You might get a warning if you’ve not been there before.
2. The preferences you’ll need to set are these:
   

   Key	Set it to
   mailnews.default_news_sort_order	2
   mailnews.default_news_sort_type	18
   mailnews.default_sort_order	2
   mailnews.default_sort_type	18
   mail.delete_matches_sort_order	true

3. The final step is to stop Icedove and then delete any .msf files from your ~/.icedove/xxxxxxxxx.default folder. These cache folders and hence won’t reflect your changes.

WTF? Why did that work?

I had a look at the Mail and news settings reference. It looks like the various sort_order keys can be 1 or 2 for ascending or descending sort respectively. But that document does not tell us what the values for sort_type can be. After some faffage and fiddling I came up with a simple guide to the possible sort_types.

mailnews.*sort_types

The last setting, mail.delete_matches_sort_order is a boolean and you want it set to true for intuitive behaviour when you delete an email.