iPad and iPhone not recognizing.html file but MacMini and windows will

I sent an email with a .html file to my iPad, iPhone and Mac Mini. The Mac Mini opens the file automatically in Safari and works fine. The iPad and iPhone will not automatically open the .html in Safari. It will only open and show the .html page, it does not operate like it should open in the browser (safari). Is there a particular setting in the iPhone and iPad to allow this to work like the Mac Mini ?

And what relevance has this on a Particle community forum?

Seems to me to be a pure Apple issue.