Rick Hunter, who played the Postal Dude in the previous two Postal games, dropped out from voicing him in the third installment. This was due to personal reasons at the time as Hunter was going through a "major" break-up with a girl. Despite the developers hoping to have him back, they cast Corey Cruise, who had provided voice work for other Postal content and was also good friends with Hunter.

Postal III was delisted from Steam on November 22, 2022 due to issues with the Steam version's DRM going offline. On October 12, 2023, Running With Scissors announced on the "I Regret Nothing Podcast" that the game had received some DEPOS updates to fix the issues keeping the game from being playable, and would be added back on Steam at a later date with some additional fixes from the ZOOM Platform version of the game.

On January 29, 2024, the Steam version of Postal III received a large content update adding various features and improvements originally made by the developers of the Zoom Platform version of the game as well as fixes and content by the series' fan community. The update notably included streamlined mod support, a high quality release of the official soundtrack, several bug and graphical fixes pointed out and contributed by players, updated versions of the game's official German and Japanese localizations, three new localizations in Portuguese/Brazilian, French and Polish translated by fans, and worldwide access to the previously Russian-only Fart Gun DLC.