20 years ago we use to do faxes. At that time, faxes was just entering the business field. Allot of business did not have a good enough quality fax or it was only 7,200 k. When emails started to get more user friendly back 9 years ago, we went to the billing via emails.
Now I do nothing but emails. In fact, we discounted our fax number all together some years back.
The benefits of an email shows when the bid / contract was sent out ( All 27 pages ). It also shows when the invoice was sent. This is important due to finance charges. We charge 35 days from the receipt of the email for billing. At 1.5% per month, it adds up. Plus there is no " we never received the bill".