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