Exchange 2016 with Outlook 2016 and external http proxy

Hi Experts,

some our customers uses Exchange 2016, Outlook 2016 and a external http proxy Server which is written down in Internet Explorer "proxy settings".

If I instruct a user to open a shared calendar from another user a error message appear "... the resource is not available...". I deactivate the IE proxy setting, map the shared calendar and it function even if proxy settings in IE are re-activated. It's unambiguously a Problem with the proxy settings.

I tried it with different bypass-lists, unfortunately, without success, i.g.

netsh winhttp set proxy "external-proxy-fqdn:port" bypass-list="*.contoso.com; 192.168.*; *.local ..."
 // (*.local internal AD-FQDN, *.contoso external FQDN, 192.168.* internal IP Range)

How would the proxy entry have to be built up with it it functions?

Thx
reredok