Error with Proxy server and private domain

[simchgab]

Hi, good afternoon. 

I need connect to "tradersglobalgroup-demo" server in my work. I'm behind a proxy server and a institutional domain of my work. 

The parameters in metatrader 5 client is correctly configured, I can connect with Metaquotes demo accounts and ICMarkets per example, but when I try to connect with "tradersglobalgroup" for some reason the proxy server log show it's trying connect to "tradersglobalgroup-demo.my-institutional-domain:443 (attached image) this provoque a 503 error. Can anyone help me? we don't have idea what's occurs. 

In my house or smartphone don't have any issues, we don't have any idea wich provoque this error.

Very thanks