DMARC authentication error when sending from iCloud using iPhone mail app

If you are using an email address ending in @icloud.com, @me.com, or @mac.com, this issue is unlikely as Apple manages those settings.

If you are using a custom email domain (like @yourcompany.com) through iCloud+, the DMARC error usually points to a failure in your domain's DNS records, specifically with SPF or DKIM alignment.

Steps to Fix the Error

The solution involves verifying and correcting the DNS records for your custom domain at your domain registrar (e.g., GoDaddy, Cloudflare, etc.).

Check SPF and DKIM Records:

SPF (Sender Policy Framework): Your SPF record must include the iCloud mail servers as authorized senders for your domain. It should typically include include:icloud.com.

DKIM (DomainKeys Identified Mail): You should have a DKIM CNAME record that points to the Apple/iCloud mail servers, which allows them to digitally sign your outgoing emails.

Action: Ensure the MX, SPF, and DKIM records exactly match the settings provided by Apple/iCloud when you set up the custom domain. A single typo or omission will cause authentication to fail.

Verify DMARC Record Alignment:

DMARC (Domain-based Message Authentication, Reporting, and Conformance): For DMARC to pass, the domain in the visible "From" address (your custom domain) must align with the domain authenticated by either the SPF or DKIM check.

Action: Confirm your DMARC DNS record is correctly published. A common starting record looks like: v=DMARC1; p=quarantine; (or p=reject once you are confident in your setup).

Check DNS Propagation:

After making any changes to your DNS records, there can be a delay (up to 48 hours, but often less) before the changes are recognized worldwide.

Action: Use an online DNS checking tool (like MXToolbox) to verify that your SPF, DKIM, and DMARC records are correctly published for your domain.

Hope this helps.

"DMARC authentication, which stands for Domain-based Message Authentication, Reporting, and Conformance, is an email security protocol that helps protect a domain from email spoofing and phishing attacks. It builds upon two existing email authentication standards: SPF and DKIM."

"How DMARC Works

DMARC allows the domain owner to publish a policy in their DNS records that tells receiving mail servers what to do with messages that fail authentication checks. For a message to pass DMARC, it must satisfy two main conditions:

SPF or DKIM Check: The email must pass either the Sender Policy Framework (SPF) check or the DomainKeys Identified Mail (DKIM) check.

Alignment Check: The domain used in the "From" header (what the recipient sees) must align (match or be related to) the domain verified by either SPF or DKIM.

If a message fails both the SPF/Alignment and DKIM/Alignment checks, the receiving server applies the domain owner's specified DMARC policy."

"DMARC Policy and Reporting

The DMARC policy is published as a DNS TXT record and contains instructions for receiving mail servers.

Policy Actions (p=)

The domain owner specifies one of three actions for emails that fail DMARC:

p=none: Monitoring only. No action is taken on the email, but the domain owner receives reports. This is the recommended starting point for testing.

p=quarantine: The receiver is asked to treat the email with suspicion, typically by sending it to the recipient's spam or junk folder.

p=reject: The receiver is asked to outright deny the message, meaning it's not delivered at all.

Reporting

DMARC also includes a reporting mechanism, providing the domain owner with valuable insight into email traffic using their domain:

Aggregate Reports (rua=): XML reports sent daily that summarize DMARC results (which IPs are sending mail, how many pass/fail, and why).

Forensic Reports (ruf=): Near-immediate failure reports (less common now) that provide details about individual messages that failed authentication.

DMARC's power comes from its ability to not only enforce authentication but also to provide feedback that helps domain owners identify and fix issues with legitimate mail, and block fraudulent senders."