RFC 5321, as well as RFC 2821, states that non-delivery reports (bounces) must be sent to the "originator" as "indicated in the reverse path" after an MTA accepted the responsibility for delivery. However, the bounce message may be suppressed when the original content is "hostile" (cf. spam or virus mail) or the message is forged (RFC 5321, Section 6). Note that all current forgery detection methods require the mailbox owner to supply information for them to work. Failing to supply the criteria should not make any bounce message classifiable as backscatter, although some people mistakenly think it should.