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