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