[shinigami]

Sure. But what authenticates the contract? Do you sign and scan them?

[icedchai]

PDFs with e-signatures are very common place now. Have you heard of DocuSign or other similar services?

[couchand]

And so it is the e-signature, not the DKIM that matters.

[icedchai]

A signed and scanned PDF is also commonly used, same as an old-school fax-based contract where you sign and send it back. But, yes, the DKIM definitely does not matter for contract purposes.