Check your domain's
email health
Audit SPF, DKIM, DMARC, MX records and blacklist status for any domain. Enter an IP address to check blacklists, reverse DNS and hostname health.
Complete Email Infrastructure Analysis
Everything you need to diagnose and fix email deliverability issues — all in one free tool.
SPF Record Check
Validates your Sender Policy Framework record to prevent email spoofing. Detects hard fail (-all), soft fail (~all), and neutral policies.
DKIM Detection — 106 Selectors
Scans 106 DKIM selectors covering Google Workspace, Microsoft 365, Amazon SES, SendGrid, Mailchimp, Mailgun, Postmark, Zoho, and dozens more.
DMARC Policy Validation
Checks your DMARC record for reject, quarantine, or none policies. Ensures your domain is protected against phishing and spoofing attacks.
MX Record Lookup
Verifies your mail exchange records, checks for redundancy with backup MX servers, and resolves MX hostnames to IP addresses for blacklist scanning.
34+ Blacklist Check
Scans your IPs against Spamhaus ZEN, Barracuda, SpamCop, SORBS, UCEPROTECT, Invaluement, CBL, DroneBL, SpamRATS, BlockList.de, and 24 more DNSBLs.
Reverse DNS & IP Check
Enter any IP address to check PTR records, forward-confirmed reverse DNS (FCrDNS), hostname resolution, and full blacklist status.
What is an SMTP Checker?
An SMTP checker is a diagnostic tool that analyzes your domain's email configuration and mail server health. It verifies that essential DNS records like SPF, DKIM, and DMARC are properly configured, checks if your mail server IPs are listed on spam blacklists, and validates your MX records for proper email routing. The LexLab SMTP Checker performs all of these checks instantly and provides a health score out of 100.
Why Email Authentication Matters
Without proper SPF, DKIM, and DMARC records, your emails are more likely to land in spam folders or be rejected entirely. Email authentication proves to receiving mail servers that your messages are legitimate and haven't been tampered with. Major providers like Gmail, Outlook, and Yahoo now require DMARC authentication for bulk senders. Use this free tool to check your setup and improve your email deliverability.
Frequently Asked Questions
What does this SMTP checker test?
It tests five core areas: SPF records (sender authorization), DKIM records (email signing across 106 selectors), DMARC policy (spoofing protection), MX records (mail routing), and blacklist status across 34 DNS-based blacklists. For IP addresses, it also checks reverse DNS (PTR) and forward-confirmed reverse DNS (FCrDNS).
How many blacklists do you check?
We check 34 DNS-based blacklists including Spamhaus ZEN (SBL, XBL, PBL), Barracuda, SpamCop, SORBS (5 zones), UCEPROTECT (Levels 1-3), Invaluement, CBL, DroneBL, NiX Spam, SpamRATS (3 zones), BlockList.de, PSBL, WPBL, Mailspike, JustSpam, Backscatterer, Lashback, and more.
Can I check an IP address?
Yes. Enter any IPv4 address to check it against all 34 blacklists, verify its reverse DNS (PTR record), validate forward-confirmed reverse DNS (FCrDNS), and see what hostname the IP resolves to. This is essential for diagnosing mail server deliverability issues.
What DKIM selectors do you check?
We scan 106 DKIM selectors covering all major email service providers: Google Workspace, Microsoft 365, Amazon SES, SendGrid, Mailchimp, Mandrill, Mailgun, Postmark, Brevo, Zoho, Protonmail, Fastmail, HubSpot, Klaviyo, ActiveCampaign, Sparkpost, Salesforce, Zendesk, ZoneMTA, cPanel, Mimecast, and many more.
What is a good email health score?
A score of 80-100 (Grade A) indicates excellent email configuration. 60-79 (Grade B) means your setup is good with minor improvements possible. 40-59 (Grade C) suggests several issues that need attention. Below 40 (Grade D) indicates critical problems that are likely affecting your email deliverability.
Is this tool free?
Yes. The LexLab SMTP Checker is completely free to use with no signup required. Check as many domains and IP addresses as you need.