DKIM makes no assertions about the timestamp. It can be anything you want, just as in any other email.
The signature can confirm parts of the email were not edited after it was signed, not that any of the contents were ever true or correct.
The signature can confirm parts of the email were not edited after it was signed, not that any of the contents were ever true or correct.
Cheaper than paying for a digital signing service, but I imagine it wouldn't hold up as well in court.