Webmail webmail.example.com shows the blank page or the default plesk page.
DNS records for webmail.example.com is managed by external DNS server:
# dig +short webmail.example.com @18.104.22.168 203.0.113.2
There is another IP 203.0.113.3 is set in web server configuration file for webmail.example.com:
grep VirtualHost /etc/httpd/conf/plesk.conf.d/webmails/example.com_webmail.conf | grep -v "/VirtualHost"
grep VirtualHost /etc/apache2/plesk.conf.d/webmails/example.com_webmail.conf | grep -v "/VirtualHost"
Both IP addresses belongs to the server
IP address that is set for domain does not match the one specified on registrar’s side.
Log into Plesk
Browse to Home > Domains > example.com > Web Hosting Access and change IP address to the correct one 203.0.113.2
If the domain has no hosting and used only to serve mail, Web Hosting Access link is not present in Plesk. However, to update IP for webmail’s configuration file is possible via command line:
Connect to the server using SSH
Update the IP address to correct one:
# plesk bin subscription -u example.com -ip 203.0.113.2