How many legit businesses would not include a return postal address on their snail mail? Why do people expect customers to go to their home page and look for a contact form? Joss has a point.
How many postal mailboxes do you know that trigger automated out-of-office responses and all the other noise?
Bounces do happen in postal mail, but 1) the PO usually has the option to discard marketing mail instead of bouncing it, and 2) the sender has a much higher incentive in wasted postage cost to avoid bounces in postal mail, as compared to an email bounce of a few packets.
