I miss settings of priority when typing and sending new message.
I am used to use normal / high priority (red “!”) / low priority (blue arrow down).
I do not see this option at K9.
I miss delivery receipt (request for automatic confirmation about delivering into recipient’s mailbox; confirmation sent automatically by recepient’s server).
Menu item “Read receipt” is confusing since it does not indicate if it is switched off, or switched on.