I have another problem.... a much bigger problem. After the update to 2.2.13 all mail to accounts with the spam filter activated and the policy to not accept spam, was deleted. As if the spamfilter was tagging all mail as spam.
A lot of mail is send to bit-heaven....
After restarting the server the problem seemed to be solved and mail is accepted again.
The problem with the folders not available is now also fixed.