Hello

At the National Cyber Security Centre in the UK we're supportive of the PSD 
DMARC initiative. However, we currently have one problem that would hamper its 
applicability to our use case: We essentially have the need to express 
different subdomain policies to existing and non-existing domains. In our case 
for the gov.uk PSD we'd like to be able to set a 'reject' policy for 
non-existent subdomains to prevent delivery of email from them whilst not 
interfering with authentication of email for the legitimate subdomains.

Why? Well, whilst we have a programme of work to get domain owners under gov.uk 
to implement DMARC and other standards, it will take some of them time, and we 
don't want to inadvertently break mail delivery for the organisations that have 
e.g. implemented SPF but not DMARC. But on the flipside, we also know that 
non-existent domains under gov.uk are being spoofed for phishing, so we want to 
publish a policy of 'reject' on those and receive reporting about them.

What would be the best way to incorporate this requirement?

Thanks in advance


Richard Crowther, NCSC

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