Mail.App, Rules, Regular Expression, or Content Search, Base64

Will Mail.App (on Mojave) search the base64-encoded parts of a message with mail rules? It looks like he's only looking for the text.

I'm not trying to decode the base64, but just look for some base64 raw extracts provided by my rule in the base64 encoded sections.

My goal is to check if specific words have been included in a Base64 encoded HTML email.

It seems that ignores sections encoded in base64 when searching for emails via rules.