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