WireDoc [1] is a service I've used a few times that has an interesting mechanism where a party with an account on the system can send or request to receive files from another party that doesn't have an account.
I'm a former wiredoc customer. Their service is otherwise nice, but the file size limits have not kept up with the times. I switched to Hightail for requests and delivery about a year ago and have been a pretty happy camper.
[1] https://wiredoc.com