The Background Process Running Your Email
Most teams never think about DNS after setting it up. Yet DNS is the background process every mail server checks before deciding to accept a message.
When those settings are incomplete or misconfigured, the problem often goes unnoticed. Campaigns appear to send normally, but fewer messages reach the inbox.
DNS determines whether you are a trusted sender or just another spoofed domain. Understanding how it works is the first step toward fixing deliverability issues and protecting your sender reputation.
What DNS Does for Email Authentication
DNS, or Domain Name System, acts as a verification layer for the internet. For email, it publishes rules and cryptographic keys using TXT records that receiving servers use to confirm whether a message is legitimate. Three of these TXT records control this process:
- SPF defines which servers can send mail from your domain.
- DKIM provides a digital signature that proves a message was not altered in transit.
- DMARC aligns the first two and tells receiving servers what to do when something fails.
Together, these records form a chain of trust. If one link breaks, the entire message is treated as suspicious and may be filtered or rejected before it ever reaches the recipient.
SPF: The First Layer of Authentication
The Sender Policy Framework (SPF) is the simplest and most visible record in your DNS. It lists which servers are authorized to send email on behalf of your domain.
Example SPF record:
v=spf1 include:_spf.google.com include:sendgrid.net ~all
Breakdown:
v=spf1defines the SPF version.- Each
include:entry authorizes a sending platform or IP range. ~all(SoftFail) defines the policy for mail that fails SPF. This suggests the message should probably be rejected but leaves the final decision to the receiving server.
Tip: Many experts recommend using -all (Hard Fail) once you are certain all your sending sources are listed. This strictly instructs receiving servers to reject unauthorized mail.
Common SPF issues:
- Exceeding the 10 DNS lookup limit.
- Syntax errors caused by missing spaces or duplicate mechanisms.
- Outdated records left behind by old services.
Even a small mistake can cause legitimate mail to fail authentication checks, which leads to lower inbox placement and inconsistent delivery results.
DKIM and DMARC: Verification and Enforcement
DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to each outgoing message. The public key is stored in DNS so that receiving servers can verify the authenticity of the message.
If the key does not match, the verification fails.
Common DKIM problems include expired keys, incorrect selectors, or mismatched domains between mail headers and DNS entries.
DMARC (Domain-based Message Authentication, Reporting & Conformance)
DMARC is built on top of SPF and DKIM. It tells mail servers what to do when authentication fails and gives domain owners visibility into who is sending mail on their behalf.
Example DMARC record:
v=DMARC1; p=quarantine; rua=mailto:dmarc-reports@yourdomain.com
Explanation:
p=defines the policy when authentication or alignment fails:p=none: Collects reports but takes no action. (Monitoring mode.)p=quarantine: Instructs the server to treat the message as suspicious (e.g., send it to the spam folder).p=reject: Instructs the server to completely refuse the message. (Strongest enforcement.)
rua=specifies where aggregate reports should be sent.
DMARC Alignment is Key: For DMARC to pass, the domain used in the authentication check (the SPF or DKIM domain) must align with (match) the domain visible to the recipient in the "From" email address (the RFC 5322 "Header From"). If SPF and DKIM pass but the domains are not aligned, DMARC will fail.
A DMARC policy of none collects data but does not protect your domain. Moving to quarantine or reject provides enforcement once your underlying authentication is stable.
DNS Sprawl: The Hidden Source of Deliverability Issues
Over time, DNS zones often become cluttered. Every service, email platform, or marketing tool adds another record. Rarely does anyone remove old entries when switching systems.
The result is DNS sprawl, a slow buildup of outdated or conflicting records.
Symptoms include:
- SPF records that exceed lookup limits.
- Overlapping or conflicting DKIM keys.
- Multiple DMARC entries that invalidate each other.
- Random TXT records from long-retired tools or vendors.
When this happens, even correctly configured email can fail authentication because of how DNS lookups interact. A single misplaced character or duplicated entry can cause an entire domain's mail to fail validation.
Cleaning up DNS manually requires careful record analysis and a deep understanding of how these protocols interact. Without that expertise, it is easy to introduce new problems while trying to fix existing ones.
Simplify DNS and Strengthen Trust
Email authentication lives in DNS. When these records are properly configured, they create a secure handshake between your domain and the mail servers that receive your messages.
When they are not, your emails may appear to send successfully but never reach your audience.
MailMoxie's DNS Record Checker helps you find missing, conflicting, or outdated records in seconds and provides clear next steps for fixing them.
Check your DNS health now and protect your deliverability before your next send.