Ugh. I expect this is ETrade, not your forwarding or monkey.org. If you Show Original in Gmail (sounds like maybe you did?), the top has some info on the DKIM/SPF results and which domains/IPs were checked.

I did a deep dive on this a while ago to debug outgoing emails from my .name email address. TLDR, I had to give up that address, at least for outbound mail. 😢