It seems that members of a rival party (not the PSOE) have been delivering envelopes with voting papers inside telling the recipients that they are votes for the PP.
Fortunately, someone checked the contents of the envelopes and reported the matter to the Partido Popular.
This is not the only scam that people get up to in elections here in Spain. It is common practice for people to try and vote more than once by visiting different polling stations
In the recent General Election, one town recorded a turnout which was greater than the number of eligible voters.