Settings needed to get Mozilla Thunderbird to do the right thing.
I have used Evolution for a long time, primarily because it does the right thing for me. I have somewhat complicated email requirements due to the fact that I receive thousands of emails a day (mostly via mailing lists and many of which I may never read). I have procmail scripts that automatically put emails from mailing lists in the right place, which may mean creating new folders and definitely means that new email can appear anywhere in my tree of folders. Any email client that I'm going to use on a daily basis needs to handle this. My email lives on a server which I access via IMAP (or occasionally via a webmail client). Until recently, I thought the only desktop email client that could really served me well was Evolution. I've tried to use Thunderbird several times, but get stuck because I've been unable to get it to automatically look for new folders, to automatically scan all folders (including newly found folders) for email, and then to automatically download those emails so they are immediately accessible when I go to read them. Also, Thunderbird is really dumb about detecting email threads, so every time I get an email from someone with the subject "Hi," Thunderbird stupidly assumes it is related to some other email with the same subject.
It turns out that Thunderbird can actually do all these things, but it requires tweaking variables using a tool like about:config in Firefox. In Thunderbird, this is accessible by going to Edit/Preferences/Advanced/General/Config Editor have no idea why (some of) these options aren't user visible outside of the config tool, but here they are:
mail.server.default.using_subscription should be false to get Thunderbird to look for new folders.
mail.check_all_imap_folders_for_new shuld be true to get Thunderbird to check all those folders for new messages.
mail.server.default.autosync_offline_stores should be true to get Thunderbird to download the new messages before they are accessed. This may need to be created (right click in the table area and select New/Boolean)
mail.server.default.download_on_biff should be true. I think this helps out with autosync (may be redundant).
mail.strict_threading should be true to get Thunderbird to stop outsmarting itself with respect to subject-based email threads.
I think that covers it. I'd also like to get my google calendar synced into Thunderbird and again synced into my GNOME desktop calendar like Evolution does (there are plugins for that), but this should be enough to satisfy my critical email needs in Thunderbird.