Frequently Asked Questions
Answers to common questions about the PublicDNS MailTester.
General
What is the PublicDNS MailTester?
The MailTester is a tool that lets you send a real test email to a unique address on mailtester.publicdns.nl. It then analyzes the message and shows a score (1–10) with practical improvements for better deliverability.
Is the MailTester free to use?
Yes, it’s free for normal usage. Extremely heavy or automated usage may be rate limited to keep the service responsive for everyone.
Do you change anything on my domain or mail server?
No. The MailTester is read-only. It receives an email you send and performs validation checks. It does not modify DNS settings, mail server configuration, or registrar settings.
Using the tool
Where do I send my email?
First, create a test on the homepage. You will get a unique address like:
abcd1234efgh@mailtester.publicdns.nl. Send your test email to that address.
Why does the results page say “Waiting for email…”?
That usually means the SMTP receiver hasn’t received a message for your test yet. Common causes:
- The email hasn’t been sent (or is delayed in transit).
- Inbound SMTP (TCP/25) is blocked by a firewall or provider.
- The MX record for
mailtester.publicdns.nlis not configured correctly. - The SMTP receiver service is not running or not listening on port 25.
How long are emails and results stored?
When you create a test, you can choose how long the result should be retained. After the retention period expires, both the test and the stored message are deleted automatically.
Can I share my results with someone else?
Yes. Each test can provide a share link. Anyone with the share URL can view the same results. The share page updates automatically when a message is received (within the retention period).
Understanding results
What does the score (1–10) mean?
The score is a quick indicator based on common deliverability signals: SPF, DKIM, DMARC, DNSBL checks, and basic header hygiene. A lower score usually means your authentication is failing or incomplete.
Why is DKIM important?
DKIM helps prove that an email was genuinely sent by an authorized system for a domain and wasn’t modified in transit. Many mailbox providers use DKIM as a key signal to trust mail and reduce spoofing/phishing risk.
DKIM shows “fail”, but I’m sure it’s enabled — why?
A DKIM “fail” can happen even if DKIM is enabled. Typical causes:
- No
DKIM-Signatureheader (the message wasn’t signed). - Selector/domain in the signature doesn’t match your DNS DKIM record.
- DNS DKIM record exists, but the public key is incorrect or truncated.
- The message was modified in transit (headers/body changed), breaking the signature.
What blacklists are checked?
The MailTester performs DNS-based blacklist lookups (DNSBL) for the sending IP. The results page shows which lists were queried and whether the IP is listed, not listed, or if a lookup timed out/failed.
Privacy & security
Do you store emails permanently?
No. Emails and results are stored only for the retention period you selected. After expiration, the stored data is removed automatically.
Where can I find more documentation?
You can find more background and documentation on the main site. If you want a high-level overview of the tooling and related checks, visit the main Docs. For general questions, visit the main FAQ.