Postal 2 has very high sensitivity enabled by default, and the in-game slider has little to no effect. If you're using a high DPI mouse and you want to make the mouse controls actually work to your liking, read on.

Go to Steam\SteamApps\common\POSTAL2Complete\System and look for a file called user.ini. Open it in Notepad and hit CTRL+F and type in the following:
It will take you to the following section:
Simply edit the MouseSensitivity parameter to whatever is comfortable for you and you're done. I use a 400 DPI mouse on a 15.3' mousepad, so I set mine to MouseSensitivity=0.435000 in order to make a 180 degree turn while moving the mouse all the way across the mousepad.

Finding your ideal mouse sensitivity can be tricky, especially since there's no in-game console command and you need to suffer through the loading times each test, so good luck. Also keep in mind that Postal 2 seems to have some kind of Mouse Acceleration enabled with no way to turn it off. However, I do believe Mark C's Mouse Accel fix for Windows 7, 8.1, and 10 will fix this problem.[donewmouseaccel.blogspot.com]

To change the sensitivity settings for Multiplayer and the DLC, you will need to go into the "ShareThePain" and "Paradise Lost" folders respectively and edit the .ini files in their separate System folders. The ShareThePain .ini includes an extra setting called "MouseSmoothingMode=0", but you can safely ignore it.

Thank you for reading this short, simple guide. I'd like to give credit to "Know Your Meme" for hosting the Brendan Fraser/Gino DiGiannantonio picture, "backfixer1" for the sunglasses picture, and an unknown Steam user for the twerking Gimp screenshot (couldn't find the original source).

I regret nothing.