[blakesterz]

And someone found a good reason for it?

https://www.reddit.com/r/sysadmin/comments/1fn3f25/found_rsa...

  "So yes, in that one specific case it's actually a good idea to publish private keys - albeit expired ones."

[yatralalala]

Yup, it kinda makes sense, but I agree with other commenters there that plausible deniability is not as strong here.

[out-of-ideas]

what KittensInc wrote and quoted is basically the lengthly version of what plausible deniability covers. it is just a matter of time before a leak/hack/exploit happens; so ensuring we have edge cases covered is why those priv keys are published. DKIM uses these priv keys to the sender, not to encrypt the payload of the email to make it secret.