The Post Office is Dog River's mail centre. The denizens often meet by happenstance there while getting their mail. Its first appearance is in the Season 2 episode "Hero Sandwich".
Trivia
Hank met Heather when road construction was being done in front of the Post Office. ("Harvest Dance")
The Post Office in Rouleau, Saskatchewan is used for the show and is located at the corner of Scott Avenue and Main Street.