ARC (Authenticated Received Chain) 2025: Why Emails Lose Trust & How ARC Preserves Authentication
- Mithun GS
- Jun 2
- 3 min read
What Is ARC? (Simple, Email-Focused)
ARC = Authenticated Received Chain. It is a security system that preserves your email’s authentication results (SPF, DKIM, DMARC) as your email passes through different servers.
Every time your email moves through an email system, ARC adds cryptographic signatures that say:
✔ This email was originally authenticated
✔ Nothing important has been changed
✔ The chain of trust is valid
ARC tells Gmail, Yahoo, Outlook:
“This email is still trustworthy — don’t downgrade its reputation.”
Why Normal Emails Lose Trust (Even Without Forwarding)
Even if you don’t forward an email, messages often pass through:
Security filters
Anti-virus scanners
Spam gateways
Archiving services
Cloud filters (Proofpoint, Mimecast, Microsoft ATP)
Internal routing servers
These systems may slightly change the email.
And when even tiny changes happen, email services may think:
❌ DKIM is invalid
❌ Authentication cannot be verified
❌ Domain reputation is uncertain
Result:
📉 Lower reputation
📉 More chances to hit spam
📉 DMARC “fail” warnings
📉 Gmail “spammy sender” signals
ARC ensures this does NOT happen.
How ARC Fixes the Problem (Email Trust)
ARC creates a secure chain showing:
Original authentication (SPF/DKIM/DMARC)
What each server did
That the message is still trustworthy
When Gmail receives an email with ARC, it sees:
“ARC says the message WAS authenticated, and the chain is valid — trust it.”
So even if DKIM breaks due to scanning, ARC tells the mailbox:
“This email is fine — don’t punish the sender.”
What ARC Actually Adds to the Email
ARC adds three new headers:
✔ 1. ARC-Authentication-Results (AAR)
Shows SPF/DKIM/DMARC results from the previous server.
✔ 2. ARC-Message-Signature (AMS)
Protects the content of the message.
✔ 3. ARC-Seal (AS)
Cryptographically seals the chain so it cannot be faked.
These signatures prove the email is still authentic as it travels through systems.
Why ARC Matters for Your Emails in 2025
ARC directly improves:
✔ Deliverability
Mailbox providers trust emails with ARC, especially when DKIM is altered by automatic scanning.
✔ DMARC stability
Emails are less likely to fail DMARC due to scanning, routing, or internal hops.
✔ Brand reputation
Fewer false spam flags = higher sending reputation.
✔ Security transparency
Mailbox providers understand the email's history.
✔ Compatibility with modern filtering systems
Most security gateways modify emails — ARC ensures they don’t break the message trust.
ARC Example in a Real Email
You might see:
ARC-Seal: i=1; d=yourdomain.com; ...
ARC-Message-Signature: ...
ARC-Authentication-Results: ...
If these exist → your system supports ARC.
ARC Setup Requirements
ARC works like DKIM and uses DNS for public keys.
1. Generate ARC keys (like DKIM keys)
A private key stays on your server.
2. Publish ARC public key in DNS
Example:
arc1._domainkey.yourdomain.com TXT "v=DKIM1; k=rsa; p=BASE64PUBLICKEY"3. Enable ARC signing on your mail server
Most modern MTAs support ARC:
Stalwart Mail Server
Postfix + OpenARC
PowerMTA
Halon
Google Workspace
Microsoft 365 (partial)
ARC vs DKIM vs DMARC (Simple Table)
Protocol | Purpose | Problem | ARC’s Benefit |
SPF | Validates sending IP | Breaks when message moves | ARC keeps original pass |
DKIM | Validates message integrity | Breaks when content changes | ARC protects authentication |
DMARC | Combines SPF + DKIM + alignment | Fails when SPF/DKIM break | ARC tells mailbox to trust message |
ARC | Preserves authentication across systems | None — it fixes the issues | Better deliverability |
ARC = the glue that keeps SPF + DKIM + DMARC working in real-world email systems.
Common ARC Problems
❌ DNS key not published
❌ Wrong selector
❌ ARC chain broken due to tampering
❌ Server not signing ARC headers
❌ Duplicate ARC headers (bad configuration)
Fixing these immediately improves inbox placement.
Short Summary
ARC protects your email’s authentication (SPF, DKIM, DMARC) as it moves through filters and security systems.Even if DKIM breaks, ARC proves the email was originally legitimate, improving deliverability and trust in Gmail, Yahoo, Outlook, etc.
ARC = a must-have for modern email infrastructure in 2025.
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