Opt-in procedure ( §7 II UWG )  complies with EC-legislation. The required customer-confirmation
needs to be documented by the company ( this requires in case of electronical communication  recording and printing of the complete email for every single customer.
The email has to confirm the identity of the contacted consumer as well ).
In case of double-opt-in procedure ( confirmation by customers to accept any contact  , further inquiry by the company and second confirmation by the customer )
customer has the burden of proof if he contest his identity "