Dear RaSa,
Regarding to your question I have some suggestions:
1 Verify whether there's incorrect host file entry for server name
If there is please remove it.
2 Verify whether you have a file named w3wp.exe.config under c:\windows\system32\inetsrv\w3wp.exe.config.
If you do please delete this file.
3 netsh winhttp>show proxy
detect that whether there is a proxy set & used by WinRM
Remove or Adjust the Winhttp proxy to exclude the exchange servers from this configuration
Netsh winhttp set proxy proxy-server="x.x.x.x:8080" bypass-list="*.contoso.com"
Rowen
TechNet Community Support
