where to twinkle this email template problem: background: url() replaced?

Hello. I have a very cute email template (HTML file) with picture
reference to my website. I don't want to send an email with dozen (12+)
of pictures.

I learned I should use moz-not-send property to prevent mozilla from
shipping referenced picture with the email. But if the email is in
stylesheet what should I do?

In my template:

body { backgroud: url(http://my.web.site/mybg.png) }

but when the mail is sent the mail source changed to:
body { background: url(<a class="moz-txt-link-freetext"
href="http://my.web.site/mybg.png">http://my.web.site/mybg.png</a>) }

Which, of course made the recipient unable to view the picture. It looks 
like it is possible to turn off url to <a> tag translation, but how?

I believe I'm not the first one who met the problem. How do you fix this?