Trend Micro This document describes options that extend protections offered by DKIM. These options include Binding-Advice & Role-Assertion, Opaque- Identifier, and an In-Channel check. The Binding-Advice & Role- Assertion offers guidance in isolating the source of a message, in addition to establishing message signature expectations. The Opaque- Identifier (O-ID) offers protection from replay abuse and intra- domain spoofing, even when email-addresses are not associated with the signing-domain. The In-Channel check provides a means to mitigate DNS lookups for avoiding possible message replay abuse.