Yes, This is not because of network and firewalls blocking.
Let me describe in details please.
In my area Telegram is filtered and only be accessible via MTProto Proxy. ( http/https/Socks/ not working on Telegram app/desktop both )
My zammad hosted on a Hyper-V over a dedicated windows server2016. ( both are in a same network and same firewall configurations )
In Windows 2016 server telegram desktop can be connect only if i use a MTProto Proxy ( Notice all other type of proxies http/socks not work )
Now ! In zammad there is not any option that i force it to use a MTProto Proxy for telegram messaging and this is my big issue. My telegram bot not working!
If you try proxy option in zammad( Proxy Settings/Network/Settings ) , You will notice there is not any option for a MTProto Proxy.
For example i tried ( This is a real MTProto Proxy ) :
Online-MTP.dynu.net:80:f207f3a3ffd77b5b2ab874709d461e62
Hostname: Online-MTP.dynu.net
Port: 80
Credentials: f207f3a3ffd77b5b2ab874709d461e62
And click on “Test Connection” zammad will response : "Error #<ArgumentError: Failed to open TCP connection to Online-MTP.dynu.net:80:f207f3a3ffd77b5b2ab874709d461e62 (service name too long (35))>