I just started using K9 and find it does not save copies of my sent emails in the sent folder. How can change that?
K-9 Mail uploads messages to the designated Sent folder by default. You can configure which folder that is under
Settings > [Account] > Folders > Sent folder. It’s also possible to disable uploading (because e.g. your mail provider already saves a copy of the message automatically) under
Settings > [Account] > Sending mail > Upload sent messages.