I like the kmail interface, but I've had problems with it for years and in the last few days it has become unusable: it keeps locking up or crashing and there's no solution on the 'net. I won't go into details as I'm sick of it.
I tried reseting its settings (https://forum.kde.org/viewtopic.php?f=20&t=97754) to no avail. I want to move Thunderbird, but I haven't found a way to import the messages/accounts/filters: In Thunderbid the [Tools][Import] then [Next] brings me to an empty window with only [Cancel]. From kmail I managed to export everything to a zip export file, but I don't know what to do with it.
I searched for import add-ons for thunderbird without success. I've read some messages that say to move the /cur/ directories manually but that's only for the messages, right ? Any advice ?
I finally found a solution. Like Timothy Truckle wrote, I used the export/import plugin, BUT before that, I had to rename the mail files, otherwise the import would only show empty directories.
First, find where kmail stores your messages (there may be more than one place if you have several accounts):
Then in EACH of those directories, do ALL of the following:
Now you could stop here and go import the directories in Thunderbird, but you will end up with a lot of empty directories and misnamed directories, such as .Friends.directory or .Family/cur, so a little scripting can clean things up first.
Finally, in Thunderbird, create a directory IMPORT under Local Folders, select it (don't forget as right-click is not enough!), right-click on it, [ImportExportTools], [Import all messages from Directory, also its subdirectories], and let it work for a while.
I could write a script to do all of the above, but now that I've finally managed to move my mail, I'm just fed up with it.
Thunderbird has an export/import plugin where you can import mail message fom KMail folder structure. https://addons.mozilla.org/de/thunderbird/addon/importexporttools/
Unfortunately you cannot import the folder structure and the mail messages at the same time (at lease I could not).
I accidentally imported the folder structure but without any mails, so is deleted it. Unfortunately I could not reproduce that so that I had to recreate my folder structure in TB from scratch.
Then you have to import the mail messages for each folder separately. The menu of the TB import/export plugin does have "with subfolders" entries but they did not work for me.