Unable to open the Webmail going to Domains > example.com > Email Addresses > Webmail, it might show one of the following error messages:
The requested URL /roundcube/index.php was not found on this server.
Apache Server at webmail.example.com Port 80
404 - File or directory not found.
The resource you are looking for might have been removed, had its name changed, or is temporarily unavailable.
HTTP 404. The resource you are looking for (or one of its
dependencies) could have been removed, had its name changed, or is
temporarily unavailable. Please review the following URL and make sure
that it is spelled correctly.
Requested URL: /default.aspx
Plesk default page
Going to Domains > example.com > Web Hosting Access > The IP address assigned to the domain example.com in Plesk is 203.0.113.3
The DNS record for the webmail DNS record
webmail.example.com resolves to a different IP address.
# dig +short webmail.example.com
Note: After applying the changes in a DNS zone, it might take up to 48 hours to propagate the changes on global DNS servers