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