Are there any guides or tips and tricks for planning a migration from Thunderbird to KMail? The wiki did not have anything.

I don't know anything specific to KMail, but if you're using IMAP, there's not really anything to migrate.  Just set up the account in KMail and let it download.  If you're using POP in Tbird, you'd first have to set up an IMAP account in Tbird, move or copy the mail to the IMAP account, and let it upload.

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