This was the question to the customer service department of my bank:
Please can you tell me how I obtain an electronic signature for email?
And this was the answer
According to 16 article minister rule law ECO/734/2004 of march 11 about departament bank clients (B.O.E. 24/03/2004), we inform you that to attend your consult you need to have electronic signature according to the rules law 59/2003 of december 19, about electronic signature (B.O.E. 20/12/2003).