Our environment: Forest A with exchange 2010 Forest B with exchange 2007 Forest A establish two-way trust with Forest B The cross-forest availability service used to work, now in Forest B Exchange we introduced one new Exchange 2007 server with HUB+CAS+MBX server role, now user from forest A reported they can NOT see Free/Busy from Forest B, after looking into the event log of exchange 2010 server from forest A, many evet 4001 logged with below: Could not establish trust relationship for the SSL/TLS secure channel.. The request information is Discovery URL : https://NEWEXCHANGE2007.domainb.local/Autodiscover/Autodiscover.xml it turns out the new E2k7 server is installed with self-signed certificate, now we installed the same certificate with the other CAS server in forest B, but the same error still ogged on Exchange 2010 CAS server in forest A. Any one has any idea on how to fix it? thanks.

I suspect your problem is the self-signed certificate. Replace it with a public UCC certificate.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

I suspect your problem is the self-signed certificate. Replace it with a public UCC certificate.Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

Replace the self-signed certificate with a third party certificate already, still same issue. run cmdlet "get-clientaccessserver | fl" found out the newly built exchange CAS server has a different AutoDiscoverServiceInternalUri property than the other two CAS server, has requested this properties to be reset as the other two. waiting for the result

Problenm fixed with two below steps. 1): Installed certificate on newly built CAS E2k7 server. 2): Change the AutoDiscoverServiceInternalUri property of new E2k7 CAS server

Problenm fixed with two below steps. 1): Installed certificate on newly built CAS E2k7 server. 2): Change the AutoDiscoverServiceInternalUri property of new E2k7 CAS server