What DMARC does
DMARC tells receivers what to do with email that claims to be from your domain but fails SPF and DKIM: nothing (p=none), spam folder (p=quarantine) or refuse it (p=reject). It also asks them to send you reports.
It lives in one TXT record at _dmarc.yourdomain. Gmail and Yahoo ask bulk senders to publish one.
Moving to a stronger policy
Start with p=none and a rua= address to receive reports. Once they show only your own services sending as you, move to p=quarantine, then p=reject.
A subdomain without its own record follows its parent's, through the sp= tag when there is one.
Questions
What is a good first DMARC record?
v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com, published as a TXT record at _dmarc.yourdomain.com.
Does p=none protect me?
It blocks nothing; it gives you reports. It is the right start, not the end: tighten it once the reports are clean.
Will DMARC hurt my cold email?
Not when SPF and DKIM are set up for every service that sends as you. It helps: receivers trust a domain that protects itself.
What are rua reports?
Daily summaries from receivers of who sent email as your domain and whether it passed. A free report reader makes them easy to scan.
Where Coolie comes in
A domain that passes these checks is the start. Coolie then sends from your own mailboxes and LinkedIn accounts, paced over working hours, with daily caps per account and per action, a pause when someone replies and an unsubscribe line: how Coolie protects deliverability.