When it comes to giving a Christmas gift to the mail carrier, there are certain rules and regulations that must be followed in order to comply with the Standards of Ethical Conduct for Employees. Mail carriers and other USPS workers should never accept cash or gifts of substantial value from customers they serve. Any other Christmas gifts should be at most $20. Keep it lighthearted and non-monetary, such as a card with words of thanks to your postman. Or even a hand-crafted item created by someone's own hands.