[Enigmail] Enigmail and HTML (again)

[ryfe]

Hi every one,

I know that for many reasons using enigmail implies to use plain text.

But I notice one 'pleasant and wonderfull) 'bug' :
When I send an encrypted and signed email and when I also send an 
attachement (let say a tiny *.gif), enigmail doesn't force the 
conversation in plain text as it generally does, the mail is 
encrypted in HTML and perfectly received by the reader.

So my question is :
As I have only ONE person I send encrypted emails to and I will only 
have this person and as we both use Thunderbird and enigmail...
...Is there a way to send HTML encrypted mails ?
(I mean, without always use the painful solution of adding an 
attachement in order not lose HTML)

I Thank you all in advance for your answer, gentlemen.

Cheers

Ryfe