Email authentication is one of the most important layers of protection in modern communication. It helps ensure that messages are genuine, untampered, and sent from authorized sources — protecting both your organization and recipients from phishing and spoofing attacks.
Let’s break down why authentication matters and who checks what during the email flow.
💡 Why Email Authentication Is Important
Without authentication, anyone could send an email pretending to be you — damaging your brand reputation and enabling cyberattacks.
Properly implementing SPF, DKIM, and DMARC helps you:
- ✅ Prevent domain spoofing and phishing
- ✅ Protect your brand and reputation
- ✅ Improve email deliverability to inboxes
- ✅ Gain visibility into unauthorized use of your domain
⚙️ The Three Pillars of Email Authentication
| Protocol | Purpose | Configured By | Checked By |
|---|---|---|---|
| SPF (Sender Policy Framework) | Verifies that the sending mail server is authorized to send emails for the domain. | Sending organization (DNS TXT record) | Recipient mail server |
| DKIM (DomainKeys Identified Mail) | Ensures the message content is not modified and confirms the sender’s domain via a digital signature. | Sending mail system (adds signature) | Recipient mail server |
| DMARC (Domain-based Message Authentication, Reporting & Conformance) | Aligns SPF and DKIM with the “From” domain and defines the action (none, quarantine, reject) if authentication fails. | Sending organization (DNS TXT record) | Recipient mail server |
Authenticated Received Chain (ARC): Preserves original email authentication information by known services that modify messages in transit. The destination email server can use this information to authenticate messages that would otherwise fail DMARC.
🔄 Who Checks What — Incoming vs. Outgoing Email
| Direction | What Happens | Who Performs the Check |
|---|---|---|
| Outgoing (Your org → External) | Your mail system adds a DKIM signature, and your DNS publishes SPF and DMARC records. | The recipient’s mail system performs SPF, DKIM, and DMARC validation. |
| Incoming (External → Your org) | Your mail system checks SPF, DKIM, and DMARC for the sender’s domain. | Your organization’s mail gateway performs the validation. |
🧠 Real-World Example
📤 Outgoing Email
You send: user@maharjan-tech.com → user@gmail.com
- Your DNS publishes SPF, DKIM, and DMARC.
- Contoso’s server checks:
- ✅ SPF: Is the sending IP authorized for
maharjan-tech.com? - ✅ DKIM: Is the signature valid and unaltered?
- ✅ DMARC: Do SPF/DKIM results align with the “From” domain policy?
- ✅ SPF: Is the sending IP authorized for
If all checks pass, your mail is trusted and delivered.
📥 Incoming Email
You receive: user@phishingsite.com → user@maharjan-tech.com
Your Exchange or EOP server verifies:
- SPF (authorized sender?)
- DKIM (valid signature?)
- DMARC (alignment and policy?)
If checks fail, the message may be quarantined or rejected based on policy.
📊 Quick Summary
| Email Direction | Who Configures | Who Checks | Protocols Involved |
|---|---|---|---|
| Outgoing | Sender domain | Recipient mail system | SPF, DKIM, DMARC |
| Incoming | Sender (via DNS) | Your mail system | SPF, DKIM, DMARC |
🧭 Final Thoughts
Email authentication isn’t just a technical configuration — it’s a trust framework for the modern internet.
By properly setting up SPF, DKIM, and DMARC, you build a secure communication channel that safeguards your organization’s identity, improves deliverability, and protects your users from phishing threats.
