Symptoms
Unable to send or receive e-mails from remote mail addresses.
Customer in Plesk is unable to access Plesk Email Security extension, the following error message is displayed:
Hostname is not valid. Please set a hierarchical, dot-separated domain as the hostname!
Cause
The server hostname must be a fully qualified domain name (FQDN). The hostname may either be incorrectly configured in Tools & Settings > Server Settings > Hostname or on the side of the Linux operating system your are using (this can be checked by executing the hostname command when logged into the server terminal).
Resolution
Go to Tools & Settings > Server Settings and set a Full hostname.
If hostname already set, change it to some random one (ex. test.example.com) and then change back to correct hostname. This will trigger the change to/etc/hostnameas well.Open Plesk Email Security in Extensions > My extensions > Plesk Email Security > Open
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