When opening webmail in browser it returns error that server not found:
Firefox: "Server not found. Firefox can't find the server at webmail.example.com"
IE: "Internet Explorer cannot display the webpage"
Chrome: "Oops! Google Chrome could not find webmail.example.com"
Additionally, Horde webmail is known to display this message: "Unable to connect to webmail. Please contact us for further assistance."
Webmail is not resolving correctly in global DNS system because Plesk server is not added to name servers in registrar panel.
To verify the root cause, run the following commands in the command-line:
nslookup webmail.example.com <your_plesk_server_ip>
If the first one returns nothing ( or wrong IP address ) and the second one returns valid records, then Plesk server is not serving the DNS zone for a domain.
There are two options to resolve the issue:
add Plesk server to the list of DNS servers (contact your registrar);
CNAMEDNS entry onto registered name servers.