Hi Ross,
 
Many listservers ban HTML in contributions altogether; this is in deference
to those in countries with non-English versions of either Windows or Mac OS
whose mail-reading software does not support HTML. I have the Japanese
version of Eudora, which does, but many folks here use Sony or JustSoft
mail readers and suchlike which cannot handle it. People with slightly
older systems and mail readers may similarly not be able to see HTML.
Remember, you can implant hyperlinks in E-mail in most modern mail programs
without having to write the message in HTML.