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