Android requires at least one-working Gmail that is apparently tied to the default email. Now I would like to have that email under K9 but I cannot because Android instructs me to hard-reset my device if I remove the Gmail from the default Gmail. Now the problem is that I get two notification from Default client and from K9. So how can I have all emails under K9?
You don't need to remove default Google Account or factory reset to ditch double notifications. Use any one of following methods which suits you best: