I recently had to respond to the parador system when my CC number did not go through. My very computer-savvy husband says that e-mail is relatively secure, as it is not "form" oriented, so hackers are not likely to pick out credit card numbers in the odd e-mail. Concerned about who might have access to the e-mail on the other side, I made sure to transmit my response during business hours and got a response in a secure form. So, while I wouldn't make a habit of e-mailing my cc to the masses, I felt safe to do so in this case!