Diagnostic Tools
Everything you need to diagnose a domain
MX Lookup
Check mail server records and priorities
Email Auth
Validate SPF, DKIM & DMARC records
DNS Lookup
Query any DNS record type
Domain Health
Complete domain health audit with scoring
Blacklist Check
Check IP/domain against 30+ spam lists
WHOIS Lookup
Domain registration & ownership details
Speed Test
TTFB, security headers & SEO checks
Status
WebDNS.uk service health monitor
FAQ
Frequently asked questions
What is an MX record?
An MX (Mail Exchanger) record is a DNS record that specifies the mail servers responsible for accepting email on behalf of your domain. Each MX record has a priority value — lower numbers indicate higher priority. When someone sends an email to your domain, the sending server looks up your MX records to know where to deliver the message.
How do I check if my domain is blacklisted?
Use our Blacklist Checker tool to instantly scan your domain or IP address against 30+ commonly used spam blacklists (DNSBLs). If your domain appears on any list, it could mean your emails are being blocked or sent to spam folders. The tool will show you exactly which lists you appear on so you can take steps to request removal.
What is SPF and why do I need it?
SPF (Sender Policy Framework) is a DNS TXT record that lists the servers authorised to send email on behalf of your domain. Without SPF, spammers can forge your domain in the From address (spoofing). Most email providers check SPF records and may reject or flag emails that fail the check. Setting up SPF correctly improves your email deliverability and protects your brand.
How do I set up DKIM?
DKIM (DomainKeys Identified Mail) adds a cryptographic signature to your outgoing emails. Your email provider generates a public/private key pair — the public key is published as a DNS TXT record, and the private key signs each email. Receiving servers verify the signature against the public key to confirm the message was not altered in transit and truly came from your domain.
What does a DMARC policy do?
DMARC (Domain-based Message Authentication, Reporting and Conformance) tells receiving mail servers what to do when an email fails SPF or DKIM checks. You can set a policy of none (monitor only), quarantine (send to spam), or reject (block entirely). DMARC also enables reporting, so you receive feedback about who is sending email using your domain.
How does the website speed test work?
Our Speed Test tool uses the Google PageSpeed Insights API to analyse your website's performance. It measures Core Web Vitals including Largest Contentful Paint (loading speed), Cumulative Layout Shift (visual stability), and other key metrics. You get a performance score out of 100 along with specific recommendations to improve your site's speed.