Mail transformation within SendMail Transformer

Hi All

I am trying to implement sendmail transformer in my publication.
Simple text mail sending works fine. I have also trying to integrate
an html in the mail content tag and its also works fine for me.

But I want my mail to be properly styled like having background images
and properly formatted. Is that possible to do that with send mail
transformer?
If yes then how can I achieve that?

Right now I am just making different html templates and then inserting
those templates into the sendmail transformers tag as data.

<sendmail:body>{my html as string}</sendmail:body>

But it does not include any css or images.

Please suggest.

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Regards
Sachin Sharma