There is nothing wrong with receiving e-mails with beautiful prayers, nor is there anything wrong with passing good prayers on. But many of these e-mail prayers are not so harmless. Some chain prayers are modeled after secular chain letters, in which superstitious language is used to suggest to the recipient that the promised "blessing" will only be given if the message is passed on. Those with a more sensitive conscience could fall into superstition. The Catechism of the Catholic Church warns us that 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). Thus, electronic chain prayers (or letters) can become an occasion of sin (CCC 2111, 1 Cor 8:13).
The Catechism of the Catholic Church says about the First Commandment: "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" (CCC 2111).