Log in to your Horde webmail client and click the [New message] button. In the "Message Composition" window that opens you will see the option [Switch to HTML composition]. Click it and a WYSIWYG editor will open, giving you the option to edit your text's font, size, format, to insert links and images, and other html entries.
Additional questions asked by Internet Explorer users:
I do not see the Switch to HTML composition / it does not work.
Please make sure you have the Compatibility View enabled for the Horde webmail; you do this by going to 'tools' in internet explorer and click the Compatibility View option.
