Student or Learner
"In regular direct mail, you can have mailers renting your list return undeliverable addresses to you."
"Addresses" are some unmovable physical locations, so "return undeliverable addresses" seems weird.
I meant to say that it is probably more logical to "return undeliverable mail" back to the sender than "return undeliverable addresses" to the sender.
Not in this context- the person has rented a list of addresses that they are mailing to, but when mail is undeliverable, they merely pass on the address the the owner of the list, not the mail. The person can then update the list.