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