10-11-2026, 12:17 PM
Reverse DNS identifies your sending server. Verify its PTR record, then send an actual message through your mailbox and review the receiving tool's authentication results.
Verified lab result, 11 October 2026: AlphaVPS configured the PTR for 217.217.235.82 as mail.adminslab.com. Public forward and reverse lookups now match, and Postfix uses that same hostname. A real Roundcube message tested with SEOStackTools Email Tester scored 95/100, Grade A: 12 passed, 2 to improve, 0 errors. SPF, DKIM, DMARC, blacklist and PTR checks passed.
1. Understand forward and reverse DNS
Forward DNS maps mail.example.com to your VPS IP. Reverse DNS maps that IP back to a hostname through a PTR record. The VPS provider controls reverse DNS for its address space. Adding a PTR record in your ordinary Cloudflare domain zone does not update the provider's reverse zone.
Use a stable mail hostname that resolves to the sending IP. Our lab uses mail.adminslab.com for forward DNS, reverse DNS and the SMTP server hostname.
2. Request or set the PTR
Check the VPS provider's Reverse DNS/rDNS/PTR settings. If no control is available, open a technical-support request with the VPS IP and desired full hostname. For example: Please set the PTR for our VPS IP to mail.example.com. Its forward A record already points to that IP.
No root password is needed for a PTR request. After the provider confirms, check public DNS rather than relying only on the ticket's status.
3. Verify both directions
On Ubuntu, these commands query a public resolver:
The first should return the desired hostname; the second should return the sending IP. The last shows Postfix's hostname. In our lab, all three agreed. If an old result remains, allow cached DNS to expire and check again. An NXDOMAIN response means that resolver found no PTR record.
4. Test with SEOStackTools
1. Open SEOStackTools Email Tester.
2. Click Get My Test Address.
3. Copy the unique recipient shown. Each test has its own address; do not copy one from a tutorial image.
4. In your webmail, click Compose and send a normal message from the mailbox you want to test to that address.
5. Return to the tool and click Check My Score.
6. Wait for the report, then review Authentication, Content & Spam Signals, Technical and Email Headers.
Send from the server being tested to the external tester. A same-server local message cannot verify the complete external delivery path.
5. Interpret the measured result
Our report showed SPF Pass, valid DKIM and DMARC alignment Pass. Under Technical, the blacklist check was Clean and Reverse DNS was Found, identifying mail.adminslab.com for the sending IP.
The two suggestions concerned HTML/plain-text structure and a List-Unsubscribe header. This test was an ordinary plain-text mailbox message. Plain-text email is valid; multipart/alternative is useful when sending an HTML version. Unsubscribe headers apply to subscription/marketing mail and relevant bulk-sender requirements, rather than every personal reply. Review suggestions in the context of the message's purpose instead of changing the server simply to increase a score.
6. Diagnose missing messages
Check Postfix logs for the exact recipient and remote response. A queued message is still pending. SMTP 250 acceptance means the receiving server accepted it; it does not guarantee Inbox placement at every provider. PTR, authentication, reputation and content all contribute to delivery.
Current status: PTR verified and external receipt/authentication tested with SEOStackTools. External inbound delivery from another mailbox provider remains a separate test. The old pre-PTR Mail-Tester result was 8.9/10; it is historical and uses a different scoring system from SEOStackTools.
Screenshot: measured SEOStackTools report
![[Image: mail-seostack-branded-20261011.png]](https://adminsforum.com/uploads/tutorials/mail-seostack-branded-20261011.png)
Mail tutorial series
Add a Mail Domain in aaPanel Free Edition
Install SSL for aaPanel Mail Server
Configure Mail DNS Records in Cloudflare for aaPanel
Create a User Mailbox in aaPanel Mail Server
Install and Access Webmail in aaPanel Free Edition
Send and Receive Email in aaPanel Free Edition
Create Email Forwarding and Catch-All in aaPanel Free Edition
Verified lab result, 11 October 2026: AlphaVPS configured the PTR for 217.217.235.82 as mail.adminslab.com. Public forward and reverse lookups now match, and Postfix uses that same hostname. A real Roundcube message tested with SEOStackTools Email Tester scored 95/100, Grade A: 12 passed, 2 to improve, 0 errors. SPF, DKIM, DMARC, blacklist and PTR checks passed.
1. Understand forward and reverse DNS
Forward DNS maps mail.example.com to your VPS IP. Reverse DNS maps that IP back to a hostname through a PTR record. The VPS provider controls reverse DNS for its address space. Adding a PTR record in your ordinary Cloudflare domain zone does not update the provider's reverse zone.
Use a stable mail hostname that resolves to the sending IP. Our lab uses mail.adminslab.com for forward DNS, reverse DNS and the SMTP server hostname.
2. Request or set the PTR
Check the VPS provider's Reverse DNS/rDNS/PTR settings. If no control is available, open a technical-support request with the VPS IP and desired full hostname. For example: Please set the PTR for our VPS IP to mail.example.com. Its forward A record already points to that IP.
No root password is needed for a PTR request. After the provider confirms, check public DNS rather than relying only on the ticket's status.
3. Verify both directions
On Ubuntu, these commands query a public resolver:
Code:
host YOUR_VPS_IPV4 1.1.1.1
host mail.example.com 1.1.1.1
postconf myhostname4. Test with SEOStackTools
1. Open SEOStackTools Email Tester.
2. Click Get My Test Address.
3. Copy the unique recipient shown. Each test has its own address; do not copy one from a tutorial image.
4. In your webmail, click Compose and send a normal message from the mailbox you want to test to that address.
5. Return to the tool and click Check My Score.
6. Wait for the report, then review Authentication, Content & Spam Signals, Technical and Email Headers.
Send from the server being tested to the external tester. A same-server local message cannot verify the complete external delivery path.
5. Interpret the measured result
Our report showed SPF Pass, valid DKIM and DMARC alignment Pass. Under Technical, the blacklist check was Clean and Reverse DNS was Found, identifying mail.adminslab.com for the sending IP.
The two suggestions concerned HTML/plain-text structure and a List-Unsubscribe header. This test was an ordinary plain-text mailbox message. Plain-text email is valid; multipart/alternative is useful when sending an HTML version. Unsubscribe headers apply to subscription/marketing mail and relevant bulk-sender requirements, rather than every personal reply. Review suggestions in the context of the message's purpose instead of changing the server simply to increase a score.
6. Diagnose missing messages
Check Postfix logs for the exact recipient and remote response. A queued message is still pending. SMTP 250 acceptance means the receiving server accepted it; it does not guarantee Inbox placement at every provider. PTR, authentication, reputation and content all contribute to delivery.
Current status: PTR verified and external receipt/authentication tested with SEOStackTools. External inbound delivery from another mailbox provider remains a separate test. The old pre-PTR Mail-Tester result was 8.9/10; it is historical and uses a different scoring system from SEOStackTools.
Screenshot: measured SEOStackTools report
Mail tutorial series
Add a Mail Domain in aaPanel Free Edition
Install SSL for aaPanel Mail Server
Configure Mail DNS Records in Cloudflare for aaPanel
Create a User Mailbox in aaPanel Mail Server
Install and Access Webmail in aaPanel Free Edition
Send and Receive Email in aaPanel Free Edition
Create Email Forwarding and Catch-All in aaPanel Free Edition