Two US Presidents were once Postmasters (Lincoln and Truman), but only Lincoln actually performed the job. Lincoln served as the Postmaster of New Salem, IL from 1833 to 1836. What I found interesting was that in addition to his pay, he got to send and receive personal letters for free! According this piece, Lincoln would deliver uncollected mail and carry it in his hat.
The other story that this piece shares is a story that focuses on the "Honest" Abe. When his office was closed, there was some money in the till and it took awhile for the post office to collect it. A friend, Dr. Henry, was on hand when the agent called for the money (some 16 to 18 dollars) and he was afraid the hard pressed Lincoln might have spent it in the intervening months, but he produced a sock with the coins and when it was counted, it was the exact amount.