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