xyzulu that error is probably from some upstream firewall rules
That is is a good interrogative question, and so to test this, I turned-off all firewalls(server/hosting etc) and tried again, same outcome - more on this bellow...
twest what are you doing specifically to catch that error? Like did you setup a WordPress site and it's not working, or you're trying to connect to a websites database via some external app, or you hit that error while installing an app on a hosting account?
Good question, this follows the addition of a server called 'webmail.domain.com', to which I then created a website called mymail.com, then uploaded a php webmail pro script.
Everything appears to have gone as planned(page loads, loggin admin, etc), except the db part - doesn't seem to want to connect.
To further investigate this, I brought-up another VPS server(same roles), and setup Wordpress - which worked as intended - except this time, I created a customer - the initial server/website did not.
Otherwise, I can't make sense of this - it's as though the relative webserver is not connecting to its own database - I tried 127.0.0.1 as well as the eternal IP , no joy
PS, I also tried recreating the domain on another server(within Enhance), and found the same issue - Wordpress works, but no go on this script it seems