I am still struggling with my change from K9 to FairEmail.
A language setting independent of the system language would be nice. It would be easier to communicate with you about specific settings (my system language is German, so it is difficult to refer to menu entries or settings).
Independantly set "compact mode" for list of e-mails and message view. I would like to use the compact mode for the list of e-mails but "normal" mode while reading the message.
I have used K9 for many years and I get a lot of e-mails from strange senders (customers). So I am much more focused on the subject than on the sender. I often read an e-mail, reply but leave the genuine e-mail unread as a reminder.
With K9 it is much easier for me to keep track of the subjects and unread e-mails. In FairEmail it is harder for me to distinguish the read from unread e-mails and because the subject has the same color as the address it is less easy to focus on that. For me the visualization of FairEmail is more straining.
K9 uses a different background for unread e-mails. And maybe a brighter color for the subject would help. K9 is far less colorful but easier to read (my opinion after so many years). It is difficult to recommend a solution, because FairEmail is so different and it should be, it is not a K9-clone.
Maybe you have a good idea how to improve the readability.
This is no criticism of your work! I am used to K9 but I like some features of FairEmail very much.
Maybe there is a way to adapt the visualization by some options to make it easier for K9-changers.