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