Excellent. That shows debugging will not be enough and one should at least enable tracing [1] probably on both the ZuckMail and OpenSMTPD side. FB's security team should be able to replicate this on the Zuck side if someone has a current contact. I know that a few of them lurk here. I think it's the least they can do after trying to abuse my liver and luring away an amazing coworker with the beautiful blue-haired girl.

[1] - https://wiki.archlinux.org/title/OpenSMTPD#Subsystem_tracing