Well, finally I found the solution.
Now I´m using another block, Jmail, that happened to have a very similar table disposition in the DB as the email list one. I exported the contents of two of the tables from email list and imported it in Jmail block. In fact, I created two new columns en Jmail to fit all the fields from email list so that it is easier to map the table through SQL and then I deleted those two unnecessary columns.
Now it seems we have all the emails back in moodle 3 and no notice of any problem about it at the moment.
Cheers!