Hi Subhajit,
Even if you are on hybrid environment (mid-sourcing) and the applicative server uses a proxy server for outgoing connections, the applicative server (managed in your own data center) must have the urlPermission entry:
<url dnsSuffix="deliverability-app.neolane.net" urlRegEx="https://.*"/>
Then, if it doesn't work, there are 3 issues possible:
- network access blocked (proxy because you don't use direct access/firewalls)
- access denied (credentials)
- Litmus functionality not activated by Adobe team on the Adobe deliverability-app.neolane.net server(s) for your instance (they have to configure something on their part). In that case, only solution, contact them through AC extranet support site.
Network access issue
In that case, you must also check if the proxy allows the requests to this domain.
Please firstly check web.log errors details.
What you can do, if you have access to the server, is to check the access to the Adobe Campaign deliverability-app (Inbox Rendering using Litmus) server through the proxy use.
Easy way, run the browser on the applicative server, check it has the proxy use defined and type the url.
Do you face with a timeout or an access denied.
If not possible and you have access to curl tool on the server, you can check the access to AC server with parameter for proxy.
Please run this command below, if it works fine, you must get an black screen with prompt for telnet commands.
(you can't do directly telnet deliverability-app.neolane.net 443 check, because of proxy use).
Access denied issue
Of course, if you are facing an access denied, please check with Adobe team your credentials to use (login and password) and please enter it again in the Deliverability connector.
So go into the Administration>Platform>External Accounts and select the Deliverability connector:

Regards
J-Serge