First, you need K9FP because the official K9 doesn’t share his message database with external apps like Pure messenger (at least, it doesn’t share ALL required informations).
Once installed, I strongly advise you to remove the official K9… or your device will grab emails twice.
Now, for configuration :
1 – in K9FP
– configure your email account
– check you receive your emails in K9FP
2 – in the widget config panel
– disable ’email provider’ if it was enabled
– re-enable it
– choose K9FP as email provider
– choose the K9FP account
– save & exit.
The widget will rebuild his message database and, few seconds after, display your emails.
If it doesn’t, please email me a logcat just after pressing the widget refresh button. (check here for logcat)