An unknowing orphan idolizes the horse thief/mail robber who has shot his father.
Acting
Beery's baffling charisma makes you root for a literal mail thief.
Writing
The orphan thinks his dad's killer is awesome. Script commits to this.

Director
Norman Z. McLeod
Trivia, insights & behind the scenes
Wallace Beery and Marjorie Main were a popular screen team; this was their sixth film together. Studio kept pairing them because audiences loved their chaotic energy.
The title 'Jackass Mail' refers to actual mule-delivered mail in remote Western territories—a real, dying service when this was made. The film treats horse theft as more serious than murder.