Troubleshooting MX Records and PTR Configuration on Shared Servers

This guide explains the common issue of mismatched MX records and PTR (Reverse DNS) settings in shared hosting environments, and provides steps to diagnose and resolve it.

What are SPF, DKIM, and PTR Records?

SPF (Sender Policy Framework) is an email authentication method that helps prevent spoofing by allowing domain owners to specify which IP addresses are permitted to send emails on their behalf.

Example: An SPF record might look like v=spf1 ip4:192.0.2.0/24 -all, indicating that only IPs within the 192.0.2.0/24 range can send emails for this domain.

DKIM (DomainKeys Identified Mail) increases security by adding a digital signature to emails, verifying that messages haven’t been altered and originate from the claimed sender.

Example: A DKIM signature in an email header might appear as v=1; a=rsa-sha256; d=example.com; s=default; h=from:to:subject; b=…, where d=example.com signifies that the email is signed by the example.com domain.

PTR (Pointer) Records link an IP address to a domain name, enabling reverse DNS lookups to confirm the sender’s identity.

Example: A PTR record for the IP 192.0.2.1 might resolve to mail.example.com, confirming that 192.0.2.1 is associated with this domain.

PTR Mismatch occurs when the PTR record doesn’t align with the domain in the email’s MX or HELO command, which can lead to emails being flagged as spam.
Example: If the PTR record for IP 192.0.2.1 points to mail.example.com, but the email’s HELO command uses server.example.net, this mismatch can cause the email to be rejected or marked as spam.

Together, SPF, DKIM, and accurate PTR records improve email deliverability by ensuring messages are from authorized sources.

Understanding the Problem: MX and PTR Mismatch

• MX Records: An MX (Mail Exchanger) record directs email to the correct server for your domain. In shared hosting, multiple domains share a single mail server, which can complicate MX setup.
  
• PTR Records (Reverse DNS): A PTR record maps an IP address to a domain name. This is the reverse of an A record. Email servers use PTR records to verify the sending server’s identity. If the PTR record doesn’t match the domain in the HELO/EHLO command or MX record, some email servers may reject messages.
  
• The Issue: Problems arise when the MX record points to a domain (e.g., mail.domain.com) that doesn’t match the PTR record for the server IP address (e.g., vps.brandingangels.com). This mismatch can lead to emails being flagged as spam or rejected outright.
  

How to Identify PTR Records for Your IP Address

1. Using the dig Command (Linux/macOS):
   

dig -x <IP address> 

Example:

dig -x 87.98.165.207

2. Using nslookup (Windows):

nslookup <IP address>

Example:

nslookup 87.98.165.207

• Online Tool: MXToolbox Reverse Lookup

• DNS Checker

Solution: Ensuring MX and PTR Compatibility

1. Update the PTR Record: If you have control over the IP address (or can request changes through your hosting provider), update the PTR record to match the hostname in your MX record.
   
   • Example: PTR for 87.98.165.207 → vps.brandingangels.com
   • Note: Many shared hosting providers do not allow custom PTR record changes.
2. Adjust the MX Record: If you can’t change the PTR record, modify your MX record to point to the domain name in the PTR record (e.g.,vps.brandingangels.com).
   
3. Configure SPF and DKIM Records: Add SPF and DKIM records to authenticate your emails and improve deliverability.

Example SPF record:

v=spf1 a mx ip4:87.98.165.207 ~all 

• Make sure your SPF record includes both the IP address and the domain of the shared server.

Steps for Shared Server Configuration:

1. Check MX Records: Use the dig command to verify your MX records:

dig MX yourdomain.com

2. Verify HELO/EHLO Settings: In shared hosting, the HELO/EHLO command may default to the main server hostname. Ensure the sending domain aligns with this. You might need to adjust Exim or Postfix configuration if necessary.
   
3. Configure SPF, DKIM, and DMARC Records: These DNS records authenticate your email, reducing the likelihood of it being marked as spam.

If issues persist, consider contacting your hosting provider for further assistance or adjustments, as they may be able to provide insights or make necessary server-side changes. Additionally, if you’re looking for managed hosting with greater control and support, providers like Voxfor offer dependable solutions. For more details, visit our homepage.

Conclusion

Mismatches between MX and PTR records are a frequent cause of email delivery problems in shared hosting environments. The ideal solution is to align the PTR record with the hostname used in the MX record. If this isn’t feasible, adjust the MX record to match the shared host’s domain and configure SPF and DKIM records for better email deliverability.

About the writer

Vinayak Baranwal wrote this article. Use the provided link to connect with Vinayak on LinkedIn for more insightful content or collaboration opportunities.