Playbook email comes on and then flashes off as soon as the emails appear.

I have rebooted the playbook using restart and turn off and on with the same result.
If I receive an email, the email function will stay open but if I have opened all emails and turned email off and then on, it flashes off as soon as any emails appear.
All other functions seem to operate OK.

You might try and delete the email account on the Playbook , and set it up again.....