Problem with email as text and attachment

Iam getting emails in html format with no text and html attached although I set preference for incoming emails as “Prefers notes rich text” format. Earliler it was “keep in senders format” and I have changed that to “Prefers notes rich text” and after soemtime I was getting email as plain text with html attached which I wished for. But after few days, I dont know for some reason Iam now getting email in html version with no plain text or html attachment.Could someone please suggest a solution for this.

Thanks

Sunil