cannot open the file from attachments (tickets)
Yes but not IE, not supported anymore.
I don't know how much control you have but you could try changing the registration of the DNS Servername in Setup > General > Option > DNS Servername to the actual IP address of the Server to see if that makes a difference.
Would require a restart of WHD Services again.
WHD version, are you using HTTPS or HTTP, is this from an E-Mail link? Is the user a registered Client on WHD?
It's HTTPS with a red line.
our version is 12.7.9 - Build #12.7.9.8603
yes, it's registered under the client.
actually, when I open the attachment from the ticket, it shows like a picture as I shared
psbexcvm01:8081/.../download
The 8081 Port signifies HTTP Port, do you force HTTPS within Setup > General > Server Options > redirect HTTP Request to HTTPS ?
Is the machine psbexcvm01 resolvable from the Client machine ?
this is setting
No sure..