[kazinator]

Do you have a hypothesis about why someone would be re-sending these YouTube messages? One possibility is that the original To: recipient of this message is an bad actor's address. Maybe some small percentage of users will contact that address, and thereby get harvested.

[jeffbee]

I think they're trying to goose their sender reputation, but I don't know if that is going to work.

[kazinator]

Interesting; I actually thought about that too! But there are ways it could backfire, like people reporting this junk to blacklist sites. Spamcop doesn't care that what you sent is a copy of a valid e-mail from YouTube with good DKIM.