iCalendar via e-mail?

I have been unable to get Mozilla Mail to pick up

a calendar event from an e-mail attachment.
Possibilities are:
  * Attachment formatted incorrectly (I've tried several,
    and anyway some of them seem to work if you access them
    via the web browser.)
  * Mozilla Calendar doesn't know how to use an e-mail attachment.
  * ???

Any ideas on this would be most welcome.

And if anyone is able to point out an area of dense ignorance
that is clouding my view, I certainly won't take it amiss ...

I notice that Mozilla Calendar documentation does
not seem to mention vCalendar, the older format.
Since the two formats are so similar, why would one
ever implement a tool that can't read both?
Or does it, and I'm just not reading the right stuff?

Thanks,

Vic