As a toy project, I wanted to create an online service consisting of an e-mail address to which a user could send e-mails with attached pictures and it would automatically send them back to the user after having automatically removed the metadata in the pictures (something similar to this website).
It would operate with no supervision, and the emails would be deleted as soon as they were processed, with no chance for me as the administrator to see the content.
It then hit me that it might be used for nefarious purposes and could land me in trouble. If someone sent something illegal (e.g. child pornography), could I be held responsible for distributing said content, although I as a person never knew that content ever existed and only forwarding it automatically to the original sender's address?
It gets even trickier when one realises that e-mail return addresses can be trivially crafted, so Alice could send the service an e-mail claiming to be from Bob's e-mail (e.g. email@example.com) and the service would forward the information to firstname.lastname@example.org, although Bob never used the service himself. In this case, the service would actually be (unknowingly) distributing information outside the original sender.
What would be the liabilities, if any, in Spain for the administrator of a fully-automated service which forwards information without actually analysing it?