Backhanded panthermail

I think you might be referring to a playful combination of words!

"Backhanded" is an adjective that means done or given in a way that is indirect, subtle, or even slightly insulting.

"Panthermail" is a made-up word that sounds like a combination of "panther" (a large cat) and "mail" (a form of communication).

So, if I had to interpret "backhanded panthermail," I would say it's a humorous way of describing a message or communication that is delivered in a subtle, yet slightly sarcastic or backhanded way, perhaps with a hint of playfulness or whimsy.