Mailing the story:

I've used Kontact (KDE's full feature groupware app) since it was available. I used KMail on its own before that. In that time I had never (!) reset the configuration or started from a clean start. I just migrated from version to version carrying over all my settings and local mail as new version became available.

This means I went through the various epochs: when IMAP became the better supported system; grouwpare server support; akonadi; semantic search integration (both Nepomuk and Baloo) with the same configuration and data on disk.