Step 1: Login to your webmail account with Horde interface.
Step 2: Highlight on the gear icon at the top of the page, located to the right-hand side of Notes.
Step 3: Select Preferences, followed by Mail. This will open the Preferences for Mail page.
Step 4: Under the Compose column, select Composition.
Step 5: Locate the Default method to compose messages drop-down field and select Rich Text (HTML).
Step 6: Click on Save