Don't they have the same protections?
I think it's perfectly fine to download an ebook and mail somebody your harddrive for them to read it no?
I'm not sure it's legal for you to photocopy a physical book and mail them those photocopies even if you burn your book.
You typically can't just mail a hard drive: you have to share access to the account that was used to purchase the ebook.
That would likely violate the terms of service for whatever company the account was created with. Provisions against password/account sharing are pretty common.
Well, I'm not claiming it's practical; I'm just saying its the same.
Rather than mailing your friend a hard drive, you could mail them a door key and they can come over and use your computer to read the ebook or your couch to read the book.