My clients are getting "There is a problem with the proxy server's security certificate. Outlook is unable to connect to the proxy server server.sub.domain.com. (Error Code 80000000)." This is only happening from outside of the network. I have a SAN certificate with the server name above, as well as with the outside name mail.domain.com (external), autodiscover.domain.com (external), and autodiscover.sub.domain.com (internal). The error can be dismissed, and Outlook works normally afterwards.

Remote connectivity analyzer shows no errors for Outlook Anywhere or EWS. I have removed all other certificates from my Exchange server. I have verified that the internal/external URLs are correct for Outlook Anywhere, OWA, ActiveSync, AutoDiscover, etc.

Any ideas of what may be going on?

Verify what exactly happens by using testexchangeconnectivity.com portal

Hi,

Get the output of Get-OutlookAnywhere |fl, and verify the InternalHostName, it might be server.sub.domain.com instead of mail.domain.com. If its, then change the InternalHostName to mail.domain.com by running the following command,

Set-OutlookAnywhere -Identity "servername\RPC (Default Web SIte)" -InternalHostName mail.domain.com

Regards,

Mani

Hi,

First of all, please use ExRCA to test Autodiscover and Outlook Anywhere connectivity on the problematic client when the error message appears. And we can also repair the problematic users profiles.

Here is a relevant reference:

Error message when Outlook tries to connect to a server by using an RPC connection or an HTTPS connection: "There is a problem with the proxy server's security certificate":
http://support.microsoft.com/kb/923575

If you have any question, please feel free to let me know.
Thanks,
Angela Shi