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check-auth@verifier.port25.com — Email Authentication Testing Tool
3 min read
26.04.2026
The check-auth@verifier.port25.com email address is a tool provided by Port25 (now a part of SparkPost) for testing and verifying your email authentication configuration, including SPF, DKIM, and DMARC records.
For configuring the records that this tool will check, see Configuring Mail Records (MX, SPF, DKIM, DMARC) in ISPmanager and ISPmanager 6: Email Spam Fix Guide. For DKIM-specific failure modes, DKIM Temperror and "DKIM signature, not necessarily valid".
When you send an email to this address, you will receive a detailed report back about your email authentication setup. This is helpful for diagnosing configuration issues and ensuring proper email deliverability.
How to Use check-auth@verifier.port25.com
Set Up Your Email Client
- Use your preferred email client or script to send an email from your domain.
- Ensure the email is sent from the server/domain you want to test.
Compose an Email
- To:
check-auth@verifier.port25.com - Subject: (Can be left blank or set to something descriptive, e.g., "SPF/DKIM Test")
Send the Email
Simply send the email without adding attachments or extra content.
Receive the Report
Within a few minutes, you will receive a reply to the "From" address with a detailed report of the email authentication results.
What the Report Includes
The returned report contains tests and results for the following:
- SPF (Sender Policy Framework)
- Verifies if the IP address sending the email is authorized to send on behalf of the domain.
- Example output:
SPF check: pass - DKIM (DomainKeys Identified Mail)
- Verifies if the email has a valid DKIM signature and matches the public key in your DNS records.
- Example output:
DKIM check: pass - DMARC (Domain-based Message Authentication, Reporting & Conformance)
- Ensures alignment between the From domain and the SPF/DKIM results.
- Example output:
DMARC check: pass - HELO/EHLO String Check
- Checks if the SMTP HELO/EHLO hostname complies with RFC standards.
- Additional Tests
- Reverse DNS (rDNS) validation.
- Authentication-Results header validation.
Example Report Snippet
===========================================================
Summary of Results
===========================================================
SPF check: pass
DKIM check: pass
DMARC check: pass
HELO check: pass
rDNS check: pass
===========================================================Troubleshooting Common Issues
| Issue | Solution |
|---|---|
| SPF Fail | Ensure your SPF record includes all authorized mail servers: |
|
|
| DKIM Fail |
|
| DMARC Fail | Publish a DMARC TXT record in DNS: |
|
|
| rDNS Fail | Ensure the sending IP address has a reverse DNS (PTR) record matching your domain. |
Best Practices
- Use Tools for Diagnostics:
- Along with Port25 verifier, tools like MXToolbox and Mail Tester are helpful.
- Test After DNS Changes:
- Whenever you update SPF, DKIM, or DMARC records, test again to confirm proper propagation and functionality.
- Check Email Headers:
- Look at the email headers for Authentication-Results to identify any issues.
Web checkers query the public DNS records (your SPF/DKIM TXT). Port25 verifier actually receives a real email from your sending infrastructure and checks how the receiving side sees it — including DKIM-signature-on-this-specific-message and SPF result from the IP that actually sent it. Different test, both useful.
Pass-on-all-three (SPF/DKIM/DMARC) is the floor, not the ceiling. Gmail's spam filter also weighs domain reputation, content patterns, and historical complaints. A new domain or one with prior spam history can pass auth and still be quarantined. Check Postmaster Tools for the reputation score.
Standard TTL is 1 hour but many resolvers cache longer. Verify the published value with `dig +short TXT yourdomain.com` first — if dig sees the new value, Port25 will too. If dig still sees the old one, your DNS change hasn't propagated yet; waiting on the verifier won't help.
Yes — the service is run by Power MTA (acquired by SparkPost, now MessageBird) and remains free and operational as of 2025. If you don't get a reply within a few minutes, your mail server can't reach the verifier — which is itself a deliverability red flag worth investigating (likely outbound port-25 block on your network).
What is ESMTPA?
Setting Up DKIM with Exim
Message has a DKIM or DK signature, not necessarily valid: what it means and how to check DKIM
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