TN letter - faxed/e-mailed ok?

Hi All,
Does anyone know if the TN letter has to be an originial, or is a scanned/e-mailed version ok? I saw one thread on this but with only one reply.
There doesn't seem to be any mention of this on the CBP site.
Thanks

There's no legal requirement for it be an original copy, although obviously it may look more convincing.

I used Fax copy of TN letter back in 2005. no questions asked.

I've used faxed letters with no problem at all.