There are two possible causes that I know of why your friend cannot see
the diacritical marks:
1. Is that they don't have the right font installed
2. Is that they are not viewing the page with the right encoding.
To get around it, publish the document as a PDF file from Open Office and
attach that to the email, then anyone can read the PDF as the font is
embedded.
To type Pāli in OpenOffice, you need to use macros or a Pāli keyboard for
Windows.
http://homepage.ntlworld.com/pesala/Home/html/special.html
http://www.aimwell.org/Fonts/Keyboards/keyboards.html
Pali Test for encoding in this forum
āīū ḷṃṇṅñṭ