回复：NIW RFE--能用FAX的推荐信吗?

that is no problem. You can also ask him to scan the letter and send you that. Anothe option could be PDF file with electronic signature. I used the scanned one for mine since I only have 1 week to get the letter. That worked fine.
However, if you could, try to get the original one. I think that looks nicer and you do want to have the best impression. But if you couldn't, that is not big deal.
Good luck.