The best solution is to switch your webmail to roundcube, it has a built in html editor.
In the dreamhost panel -> Mail -> Webmail. “Edit” the domain and check the “Use Roundcube” box and save. This involves a DNS change so it won’t happen instantly.
If you want to take roundcube for a test drive first go to http://roundcube.dreamhost.com/ and login with your full email address for the user name.
After logging in the first time select Settings > preferences >composing messages and set use html editor to always.