Free Authentication Tools
MXToolbox
The most widely used free tool for email diagnostics:
- SPF lookup: Validates SPF record syntax and included IPs
- DKIM lookup: Checks DKIM selector records in DNS
- DMARC lookup: Verifies DMARC policy configuration
- Blacklist check: Scans 100+ blacklists
- Email header analyzer: Parses authentication results from headers
Mail Tester
Send-and-analyze testing:
- Send email to their unique test address
- Receive comprehensive spam score (1-10)
- SPF, DKIM, DMARC results included
- Content analysis and suggestions
- Free for limited tests per day
Google Admin Toolbox
Google's free diagnostic tools:
- MX record check
- SPF/DKIM/DMARC verification
- Email header analysis
- Designed for Google Workspace but works for any domain
Start with Free Tools
Free tools handle most authentication checking needs. Consider paid tools when you need ongoing monitoring, DMARC report processing, or support for complex multi-domain setups.
SPF Checking Tools
What to Check
- Record exists at correct DNS location
- Syntax is valid
- All sending sources are included
- DNS lookup limit not exceeded (max 10)
- No conflicting records
Specific Tools
- MXToolbox SPF: mxtoolbox.com/spf.aspx
- Kitterman SPF: kitterman.com/spf/validate.html
- SPF Surveyor: dmarcian.com/spf-survey
How to Use
- Enter your domain name
- Tool retrieves and parses your SPF record
- Review results for errors or warnings
- Check that all your sending IPs/services are included
DKIM Checking Tools
DNS Lookup Method
Check if your DKIM public key is in DNS:
- Need to know your selector (e.g., "google", "s1", "default")
- Look up: selector._domainkey.yourdomain.com
- Should return a TXT record with public key
Email Test Method
Send an email and check headers:
- Send to Mail Tester or your own account
- View email headers/source
- Look for DKIM-Signature header
- Check Authentication-Results for pass/fail
Specific Tools
- MXToolbox DKIM: mxtoolbox.com/dkim.aspx
- DKIM Core: dkimcore.org/tools
- Mail Tester: Includes DKIM validation
DMARC Checking Tools
What to Check
- Record exists at _dmarc.yourdomain.com
- Policy is set (p=none, quarantine, or reject)
- Reporting addresses are configured
- Alignment mode (relaxed or strict)
Specific Tools
- MXToolbox DMARC: mxtoolbox.com/dmarc.aspx
- dmarcian DMARC Inspector: dmarcian.com/dmarc-inspector
- Valimail DMARC Checker: Free lookup tool
DMARC Report Processing
Why Process Reports
DMARC aggregate reports show:
- Who is sending email as your domain
- Authentication pass/fail rates
- Unauthorized senders to block
- Legitimate sources missing from SPF
Report Processing Tools
- dmarcian: Industry leader, free tier available
- Valimail: Enterprise DMARC management
- Postmark DMARC: Free basic monitoring
- DMARC Analyzer: Detailed reports and alerts
- EasyDMARC: Free tier with essential features
Comprehensive Platforms
All-in-One Solutions
Tools that combine multiple checks:
- MXToolbox Pro: Continuous monitoring, alerts
- dmarcian: SPF, DKIM, DMARC management
- Valimail: Automated authentication management
- Agari: Enterprise email security platform
When to Upgrade
Consider paid tools when:
- Managing multiple domains
- Processing large volumes of DMARC reports
- Needing continuous monitoring and alerts
- Requiring compliance documentation
- Working toward DMARC enforcement
Email Header Analysis
How to Get Headers
View raw email source:
- Gmail: Three dots > Show original
- Outlook: File > Properties > Internet headers
- Apple Mail: View > Message > Raw Source
Header Analysis Tools
- MXToolbox Header Analyzer: Parses and explains results
- Google Admin Toolbox: Header analysis
- Mail Header Analyzer: mha.azurewebsites.net
What to Look For
- Authentication-Results: SPF, DKIM, DMARC pass/fail
- Received-SPF: SPF check result
- DKIM-Signature: Presence of signature
- ARC headers: For forwarded mail