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It's not uncommon to show a little gratitude in the form of a tip to those who make your life easier. As it turns out, USPS won't allow your friendly mail carrier to accept cash, checks, gift cards and more.

You can see for yourself from the official USPS website:

All postal employees, including carriers, must comply with the Standards of Ethical Conduct for Employees of the Exec­utive Branch. Under these federal regulations, carriers are permitted to accept a gift worth $20 or less from a customer per occasion, such as Christmas. However, cash and cash equivalents, such as checks or gift cards that can be exchanged for cash, must never be accepted in any amount. Furthermore, no employee may accept more than $50 worth of gifts from any one customer in any one calendar year period.

This isn't just Yakima, but all across the United States.

Although, yes, they can accept small gifts like a Christmas card would be perfectly acceptable. However, you can't include a $25 gift card in that letter.

Something to keep in mind.