Symptoms
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Plesk Email Security > Config check shows red RDNS indicator on subscription
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Subscription is configured to use shared IP address
Cause
The PTR record for the subscriptions IP points to the server's hostname
Resolution
This is expected behavior, as the extension only marks the rDNS record as correct if the IP is pointing to the domain itself.
A PTR record pointing to the server's FQDN is sufficient and hence, no further action is required.