Getting Started with MXToolbox
The SuperTool
The main search box on mxtoolbox.com is the SuperTool:
- Enter a domain, IP address, or email header
- Automatically detects what kind of lookup to perform
- Add prefixes for specific tests (e.g., "spf:yourdomain.com")
- Results include links to related tests
Common Prefixes
- mx: MX record lookup
- spf: SPF record check
- dkim: DKIM record lookup
- dmarc: DMARC record check
- blacklist: IP blacklist scan
- smtp: SMTP server test
Bookmark Your Domain
Create a browser bookmark for "mxtoolbox.com/SuperTool.aspx?action=mx:yourdomain.com" to quickly run checks without re-entering your domain each time.
MX Record Lookup
What It Shows
- Your domain's mail exchange servers
- Priority of each MX record
- IP addresses of mail servers
- Response time from each server
How to Use
- Enter your domain in SuperTool
- Select "MX Lookup" or use "mx:" prefix
- Review the list of mail servers
- Verify servers match your expected configuration
What to Look For
- Correct mail servers listed
- Appropriate priority values
- All servers responding
- No unexpected entries
SPF Record Check
Running the Check
- Use "spf:yourdomain.com" in SuperTool
- Or navigate to mxtoolbox.com/spf.aspx
- Tool retrieves and parses your SPF record
Understanding Results
- Record found: Shows your full SPF record
- Includes: Lists all authorized senders
- DNS lookups: Count toward 10-lookup limit
- Warnings: Issues that may cause problems
- Errors: Syntax or configuration mistakes
Common Warnings
- Too many DNS lookups (exceeds 10)
- Missing terminating mechanism (~all, -all)
- Multiple SPF records (only one allowed)
- Deprecated ptr mechanism
DKIM Record Check
Running the Check
DKIM requires knowing your selector:
- Navigate to mxtoolbox.com/dkim.aspx
- Enter domain and selector
- Tool looks up selector._domainkey.yourdomain.com
Finding Your Selector
If you do not know your selector:
- Check your email provider documentation
- Send yourself an email and view headers
- Look for "s=" in the DKIM-Signature header
Common Selectors
- Google: google
- Microsoft: selector1, selector2
- Mailchimp: k1, k2
- SendGrid: s1, s2
DMARC Record Check
Running the Check
- Use "dmarc:yourdomain.com" in SuperTool
- Or navigate to mxtoolbox.com/dmarc.aspx
- Tool checks _dmarc.yourdomain.com
Understanding Results
- Policy (p=): none, quarantine, or reject
- Subdomain policy (sp=): Policy for subdomains
- Reporting (rua/ruf): Where reports are sent
- Alignment: Relaxed or strict matching
Blacklist Check
Running the Check
- Enter your sending IP address
- Use "blacklist:" prefix or go to mxtoolbox.com/blacklists.aspx
- Scans 100+ blacklists simultaneously
Interpreting Results
- Green: Not listed on that blacklist
- Red: Listed - click for details
- Timeout: Blacklist did not respond
If You Are Listed
- Click the listing for removal instructions
- Identify and fix the cause (spam, compromise, etc.)
- Request delisting from each blacklist
- Monitor to ensure you stay delisted
Email Header Analyzer
How to Use
- Get email headers from a received message
- Paste into mxtoolbox.com/EmailHeaders.aspx
- Tool parses and explains each header
What It Shows
- Mail server routing path
- Time spent at each hop
- Authentication results (SPF, DKIM, DMARC)
- Spam scores and flags
- Delays in delivery
Key Headers to Review
- Authentication-Results: Pass/fail for each protocol
- Received: Server path (bottom is origin)
- X-Spam-Status: Spam filter assessment
SMTP Diagnostics
SMTP Test
Tests if your mail server is accepting connections:
- Enter your domain or mail server hostname
- Attempts SMTP connection on port 25
- Reports success, failure, or issues
Common Issues Found
- Server not responding
- Connection refused
- Missing reverse DNS
- Banner issues
- TLS problems