Unless this is a close personal friend or family member sending you these emails, don’t bother. Just politely request that you be taken off the bulk email list. If it is a close personal friend or family member, then gently explain that the practice is superstitious. Here is a definition of superstition from the Catechism of the Catholic Church:
Superstition is the deviation of religious feeling and of the practices this feeling imposes. It can even affect the worship we offer the true God, e.g., when one attributes an importance in some way magical to certain practices otherwise lawful or necessary. To attribute the efficacy of prayers or of sacramental signs to their mere external performance, apart from the interior dispositions that they demand, is to fall into superstition (CCC 2111).