All of a sudden the customers on my Magento webshop can't login (http://www.healthxl.eu), get confirmation mail or reset password... Also, I noticed that when I tried logging in with a wrong password it just gave me the error (see below).
I tried rolling back a backup I made last week but even this doesn't work. The error messages:
An unspecified error occurred. Please contact us for assistance. We're unable to send the password reset email.
Sorry for the not so clear question I asked there. However, after updating my Magento install from 2.1 to 2.1.2 the problem seems to be fixed.