DMARC: Domain-based Message Authentication, Reporting and Conformance
Configuring DMARC for any given domain requires only a DNS entry for that domain, containing machine-readable instructions for any message recipient to automatically authenticate an incoming message. The server receiving any message can check the "from" domain's DNS for a DMARC record. If one is found, the message will be accepted only if it passes the requirements.
The DMARC DNS entry for a given domain uses a "_DMARC" subdomain (
_DMARC.<domain>). The explanation of the DNS record contents seems to begin in section 6.3 of RFC-7489.
||how closely to check DKIM configuration ("alignment")|
||how closely to check SPF configuration ("alignment")|
|fo||n||failure [reporting] options|
|Requested Mail Receiver policy|
||% of domain's messages subject to policy
|rf||n||<list of one or more report formats>||Format to be used for message-specific failure reports
|ri||n||<number of seconds>||maximum interval between aggregate reports; default is 86400|
|rua||n||<one or more email addresses, comma-separated>||addresses (DMARC URIs) to which aggregate reports are to be sent|
|ruf||n||<one or more email addresses, comma-separated>||addresses (DMARC URIs) to which message-specific failure information is to be sent|
|sp||n||(same as p; optional)||Requested Mail Receiver policy for all subdomains; defaults to value of p|
||Version - identifies the record retrieved as a valid DMARC record. Must be the first tag.|
documentation in progress
It appears that some large email services (such as GMail) may reject messages if DMARC is not configured in a way they deem suitable; as far as I know, this is not officially documented anywhere (security by obscurity), and proper configuration can only be determined by experimentation.
For some reason, DigitalOcean apparently does not support wildcards in TXT DNS records, so you can't set up a wildcard DMARC recipient.
- 2014-04-07 Yahoo breaks every mailing list in the world including the IETF's: a problem with how DMARC is designed