The explosives, purportedly sent by a group calling itself Anticlerical Pro Sex Toys, were mailed to the Archbishop of Pamplona, Francisco Pérez and to the head of a Madrid school run by the Legionaries of Christ.
The package which arrived at the office of the archbishop in January contained a vibrator.
The police were called when the parcel was also found to contain powder.
Another device, intended for the priest in charge of Highlands School in Madrid, exploded at a postal sorting office, leaving a woman with slight injuries.
"Please accept our apologies," said an email to an anarchist website thought to be from the group. "Next time we will not fail."