According to this post you do not need /SOGo in your proxy definition. Just redirecting to https://server1 should be enough.
EDIT:
If it doesn’t work you may try it with a virtual host name instead of the path “/sogo”.
According to this post you do not need /SOGo in your proxy definition. Just redirecting to https://server1 should be enough.
EDIT:
If it doesn’t work you may try it with a virtual host name instead of the path “/sogo”.