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