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