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