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