<p>“due” is used as an adjective
“becuase of” is used as preposition
“caused” is a verbal-adjective, so it is also used as an adjective.</p>
<p>So, “do to” and “caused by” function in the same way in a sentence, which differ from “because of”</p>
<p>So it is NOTlegitimate to say :
The plan was postponed due to the rain
although I hear this sort of thing all the time -.-
If you substitute “due to the rain” with any other adjective (red/ big/ good…), the sentence does not work gramatially.
Here is the right usage:
The delay of the plan was due to/caused by the rain.
as was should be followed by an adjective-phrase here.</p>