If you see the following crash dialog, or if K-9 Mail otherwise misbehaves, you can ask for assistance from the development team.
K-9 Mail has controllable debug logging. Users can activate logging to help diagnose problems and errors.
As an open source privacy-conscious project, we don't implement an always-on logging system that reports all the device's activity to a central server. While this would make issues easier to fix it would also be costly to host the server and compromise the privacy of our users.
Instead we ask, if you find an issue, and are willing to help, you provide the logs yourself. Up-to-date instructions on logging are provided on the wiki.