Obviously the transfer agent bears the lion's share of blame here, but 'lack of printer' feels a bit helpless. It's hard to imagine that a scan of a wet signature on a printed email would be more valid than print-to-PDF and 'Add Signature' in Preview in one's own hand, or that the transfer agent would even be able to verify. One could even go the extra mile with ImageMagick[0] if they were so inclined.

Obligatory IANAL, this is not legal advice, and it's probably at least technically wrong.

[0]: https://tex.stackexchange.com/questions/94523/simulate-a-sca...