Be careful with old versions!
These versions are displayed for reference and testing purposes. You should always use the latest version of an add-on.
Thanks to JRobert for reporting the issue.
✔ Security fix to ensure no html is injected after decrypting...
Thanks to gbuk2013 for reporting it.
Thanks to JF Mayer for reporting the issue.
✓ HTML/BODY elements with the designMode attribute set to "on" should work now as well, which are commonly used by certain web-mail clients and/or to send html-formatted messages.
Thanks to Jennifer B. and Alexander L. for their help testing.