DKIM Test vs Manual DNS Lookups (nslookup/dig)

You can check DKIM records with command-line tools like nslookup or dig. But should you? Here's how manual DNS lookups compare to using a dedicated DKIM testing tool.

The Manual Approach

To check a DKIM record manually, you'd run something like:

# Using dig
dig TXT selector._domainkey.example.com

# Using nslookup
nslookup -type=TXT selector._domainkey.example.com

This returns the raw DNS record. For a DKIM record, you'll see something like:

"v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC..."

Now what? You need to:

1. Verify the record syntax is correct
2. Check if the key is valid
3. Understand what each tag means
4. Diagnose any issues

That's where manual lookups fall short.

Quick Comparison

What Manual Lookups Can't Do

Parse and Validate

A DKIM record contains multiple tags:

• v= — Version (should be DKIM1)
• k= — Key type (rsa, ed25519)
• p= — Public key (base64 encoded)
• t= — Flags (optional)
• h= — Hash algorithms (optional)

Manual lookups show you the raw record. You need to manually verify each tag is correct, the key is properly formatted, and nothing is malformed.

DKIM Test parses everything and tells you exactly what's right or wrong.

Explain Problems

When dig returns NXDOMAIN, it just means "not found." But why?

• Wrong selector?
• Selector typo?
• Record not published yet?
• DNS propagation delay?

DKIM Test provides context: "No record found for selector 'google'. Common selectors for this domain include 'selector1' (Microsoft 365)."

Check Key Validity

Even if a record exists, the key might be:

• Too short (512-bit keys are weak)
• Malformed (truncated base64)
• Using deprecated algorithms

Manual lookups can't tell you this. DKIM Test validates the actual cryptographic key.

When Manual Lookups Make Sense

Command-line tools are useful when:

• Debugging DNS propagation — Check if a new record has propagated to specific nameservers
• Scripting — Automate checks in deployment pipelines
• Learning — Understand how DKIM records work at the DNS level
• No internet access — Work in air-gapped environments

# Check specific nameserver for propagation
dig @8.8.8.8 TXT selector._domainkey.example.com

# Check authoritative nameserver directly
dig @ns1.example.com TXT selector._domainkey.example.com +short

When DKIM Test Makes Sense

Use DKIM Test when:

• Validating configuration — Need to know if your DKIM is actually working
• Troubleshooting failures — Want to understand why DKIM is failing
• Finding selectors — Don't know which selector your email service uses
• One-off checks — Just need a quick answer without terminal access
• Explaining to others — Need shareable results for colleagues or clients

The Selector Problem

Here's the real advantage of DKIM Test: you often don't know your selector.

With dig, you need the exact selector. If you guess wrong, you get nothing:

$ dig TXT google._domainkey.example.com +short
# (empty - wrong selector)

DKIM Test helps by suggesting common selectors and linking to documentation for finding yours.

Combining Both Approaches

For thorough DKIM troubleshooting:

1. Use DKIM Test first — Validate the record, check key strength, understand any issues
2. Use dig for propagation — If you just updated DNS, check multiple nameservers
3. Use DKIM Test for monitoring — Set up alerts for ongoing changes

Monitoring: The Real Difference

Manual lookups are point-in-time. You check once and move on.

DKIM Test (via the Email Deliverability Suite) monitors continuously. When your DKIM record changes—intentionally or not—you get an alert before emails start bouncing.

No cron job required. No scripts to maintain. Just set it up and get notified when something breaks.