Rebuild PTR / Reverse DNS Cache and Update Mail HELO for Email deliverability

Symptoms

After updating the PTR record for the server's hostname, Email Deliverability is still showing the old PTR record. The interface also indicates the record doesn't match.

The system uses an alternate HELO of “oldPTR.hostname.com” 
when sending mail from the “server.hostname.com” domain.

Please note that in the above example "oldPTR.hostname.com" and "server.hostname.com"  represent the previous PTR record and current hostname, respectively.

Description 

cPanel will automatically define the Mail HELO to match the PTR record for the server's outbound SMTP IP addresses. When the PTR record changes, rebuilding the cache would ensure the updated record appears in the Email Deliverability interface.

Workaround

1. Log into WHM as the 'root' user.
2. Navigate to "Home / Service Configuration / Exim Configuration Manager."
3. Click the "Domains and IPs" tab.
4. Click the "Rebuild RDNS Cache" button.

Additional resources

Exim Configuration Manager - Basic Editor - Domains and IPs