DMARC, Domain-based Message Authentication, Reporting & Conformance, an email authentication, policy, and reporting protocol.
Builds on the SPF and DKIM protocols,
adds linkage to the author (From:) domain name, published policies for
recipient handling of authentication failures, and
reporting from receivers to senders, to improve and monitor protection of the domain from fraudulent email.
Email authentication technologies SPF and DKIM provide assurance on the identity of the sender.
When senders used these technologies, receivers are able to differentiate the fraudulent messages from
ones that properly authenticated to the domain.
legitimate messages that dont authenticate and the fraudulent messages that dont authenticate.
Receivers supply senders with information about their mail authentication infrastructure while
senders tell receivers what to do when a message is received that does not authenticate.
DMARC system provides senders and receivers a means to collaborate to improve mail authentication and to reject unauthenticated messages.
DMARC and the Email Authentication Process Helps receivers determine if the message aligns with what they know about the sender and guidance on how to handle the non-aligned messages. For example, assuming that a receiver deploys SPF and DKIM, plus its own spam filters, the flow may look something like this:
from DNS
| |
author --> his receiver retrive retrieve retrieve and quartine
sends SMTP server validates DKIM envelope from apply DMARC -----^
email inserts DKIM against blacklist domains SPF reporting and ------------> reject
destinastion -----,
deliver
Authentication flowIn the above example, testing for alignment applied at the same point where ADSP would be applied in the flow.
DMARC policies are published in the DNS as text (TXT) resource records (RR) and announce what an email receiver should do with non-aligned mail example:DMARC TXT RR for the domain sender.dmarcdomain.com that reads:
"v=DMARC1; p=reject; pct=100; rua=mailto:postmaster@dmarcdomain.com"sender requests that the receiver reject all non-aligned messages and send a report, about the rejections to a specified address. For testing use p=quarantine consider quarantining it.
> Tag Purpose Sample v Protocol version v=DMARC1 pct Percentage of messages subjected to filtering pct=20 ruf Reporting URI for forensic reports ruf=mailto:authfail@example.com rua Reporting URI of aggregate reports rua=mailto:aggrep@example.com p Policy for organizational domain p=quarantine sp Policy for subdomains of the OD sp=reject adkim Alignment mode for DKIM adkim=s aspf Alignment mode for SPF aspf=r oHow Senders Deploy DMARC 1 Deploy DKIM & SPF. 2 Ensure that mailers are correctly aligning the appropriate identifiers. 3 Publish a DMARC record with the 'none' flag set for the policies, which requests data reports. 4 Analyze the data and modify mail streams as appropriate. 5 Modify DMARC policy flags from 'none' to 'quarantine' to 'reject'
| Domain publishes the signing practices when relaying mail on behalf of associated authors. Author address in 'From' header Author Domain Signature is a valid DKIM signature in which the domain name of the DKIM signing entity, i.e., the d tag in the DKIM-Signature header field, is the same as the domain name in the author address. DNS _adsp._domainkey.example.com. IN TXT "dkim=unknown" unknown domain might sign some, most, or all email,the same as not defining any record, the all all mail from the domain is signed with an Author Domain Signature, discardable says all mail from the domain is signed with an Author Domain Signature; furthermore, missing or invalid, the domain owners want the receiving server to drop the message; The specification explicitly discourages publishing a record different from "unknown" for domains who have independent users and a usage policy that does not explicitly restrict them to sending mail only from designated mail servers, since mail sent independently of the organization will not be signed. One of ADSP's authors holds that it is better to publish private lists of discardable domains, maintained by competent people, rather than letting each domain state their policy. author of a popular ADSP implementation has proposed to downgrade ADSP to experimental downgraded to historical. The consideration that DMARC covers more or less the same use case was influential, but not tied in. |
_token._dnswl.hilltopconservancy.org e1s3i8a7ajgvw6m1ce5xmxgjknj8w6ka"
default._domainkey.hilltopconservancy.org
"v=DKIM1;
k=rsa;
p=MIIBIjANBgkqhkiG9w