I recently setup a 2010 exchange server. All local emails and OWA works but when I try to connect a off site user via RPC over HTTP, I get the following error.
"There is a problem with the proxy server's security certificate. The security certificate is not from a trusted certifying authority.
Outlook is unable to connect to the proxy server domain.com. (Error Code 18)"
So the following troubleshooting steps have already been taken.
1. Reinstalling the certificate from the HTTPS://
site manually in the root auth folder.
2. Using multiple laptops at different locations. (Outlook 2007)
3. Uninstalling RPC over HTTP proxy and reinstalling it on the server.
There are no errors in the event logs or any email issues besides this. Is there any special ports that need to be opened in the firewall besides HTTPS?