Accessing a website example.com hosted on a Plesk server fails:
Accessing this website's web statistics page http://example.com/plesk-stat/webstat/ or the maillist page for http://list.example.com fails with the same error.
In Plesk in Domains > example.com > DNS Settings, NS records point to an external DNS hosting.
The IP address 203.0.113.2 is set for the domain example.com in Plesk.
However, the A record for example.com returns different IP address:
# dig example.com
;; QUESTION SECTION:
;example.com. IN A
;; ANSWER SECTION:
example.com. 3599 IN A 203.0.113.3
The A record for example.com on the external DNS hosting points not to the Plesk server.
On the external DNS hosting, change the value of the A record for example.com (and also for subdomains like list.example.com if necessary) so it points to the IP address of the Plesk server.