Differences in Hyperlinks

I had someone in another department ask why her hyperlink did not work in the
email she sent for most people. I went over to see how she was inserting the
hyperlink and she used the Insert --> Hyperlink and browsed to the file. She
is set up with Rich Text.

I realized that anyone with HTML could not click on the link. However, if
you added the hyperlink by \\ntserv etc anyone with Rich Text or HTML could
click on the link.

I'm curious, what is the difference between the various ways you can add
links so that some work with Rich Text and HTML but others will only work
with one. I want to be able to tell her the best way to insert the link so
that hopefully everyone will be able to click on it.

Thanks! Trisha