[jchook]

DMARC basically breaks mail intermediaries and is fundamentally problematic, hence the low adoption rate.

ARC is a much better alternative that builds on DKIM and allows intermediate custodians of mail.

[aj3]

No it doesn’t, unless said intermediaries are modifying contents and are not DMARC aware.

Many European countries are forcing DMARC adoption for government infrastructure and it works just fine.

[azinman2]

What does intermediate custodian mean here? Something like sendgrid? Is there an issue for normal peoples email on custom domains (eg fastmail or gmail hosted)?

[toomim]

I think he is talking about mailing list servers. When you email mailman, it'll add a line to the bottom of the email, manipulate some to: and cc: headers, and forward it along. This changes the hash of the email which breaks some crypto signatures.