The closing device of my main door causes the main door to close with a strong force, slamming it instead of closing it gently.
I pasted a notice on the main door: “Please prevent the door from slamming shut.” The reason is so that my family members would hold on to the door when they are going out or when they return home to prevent the door from closing with a bang.
I was told by a friend of mine that the “shut” was redundant. I would like to know if she is correct.
Many thanks.
I think it might be redundant; your friend is correct in that it is true that a door cannot really “slam open”. “Don’t let the door slam.” is shorter if your sign happens to be small 
Still, I think “slamming shut” sounds fine. When I Googled it, I got almost 26 million hits, so I don’t think I am the only one!
I think you can slam a door without actually closing it so I do see a difference between just slamming a door and slamming it shut.
Hi Torsten,
I wholeheartedly concur - in other words I agree!
That’s music to my ears, Alan 
So Torsten and Alan, how would the door slam without shutting? I can understand slamming your fist against the door, but that is not what people mean by “Don’t slam the door”.
Well, I think you can slam a door with various degrees of strength resulting in the door either being shut or not. You can even slam a door so hard that parts of it break and then it’s not shut.
I think you have to go back to the original question. The poster quoted the notice -
Please prevent the door from slamming shut.
It is the device on the door that is causing the door to shut and adding the word ‘shut’ to ‘slam’ makes it clear that the door is being shut violently.’ Don’t slam the door’ is another situation where it is not clear whether the door is being hit, smashed, struck or whatever. The assumption is that you mustn’t shut the door violently but writing a notice as in the post above, requires the word ‘shut’.