Here is the full list of all 25 POSTAL Redux achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Perfect all Rampage levels.
Complete all Rampage levels.
Complete every level in Co-op mode.
Complete the Excess Postage campaign in Nightmare difficulty.
Execute two of every hostile type.
Complete the Campaign having killed only hostiles.
Complete the Campaign with a total play time of 30:00 or less.
Complete the Campaign.
Complete the Campaign having left no survivors.
Finish a level with less than 10 health.
Watch the entire credit sequence.
Wipe out the game protestors in Ghetto.
Kill all Ostriches in The Farm.
Blow up 50 barrels.
Kill four or more people with a single Rocket Launcher missile.
Kill three or more people with a single Mine explosive.
Kill 30 people with the Napalm Launcher.
Duck under 10 rockets.
Earn a kill with every weapon.
Commit suicide.
Reach the half way mark of the Campaign.
When burning, set someone else on fire by running into them.
Firebomb the Marching Band.
Perform 13 executions.
Make your first kill.