I have correctly setup my autodiscover, activesync, and even split dns. But for some reason people are still seeing the security warning after they open outlook.

Hello

check all internal and external url:

Get-WebservicesVirtualDirectory -Server $ExServer |Fl internalURL,ExternalURL
Get-OWAVirtualDirectory -Server $ExServer | Fl internalUrl,ExternalURL
Get-ECPVirtualDirectory -Server $ExServer | Fl InternalURL,ExternalURL
Get-ActiveSyncVirtualDirectory -Server $ExServer | Fl InternalURL,ExternalURL
Get-OABVirtualDirectory -Server $ExServer | Fl InternalURL,ExternalURL
Get-ClientAccessServer $ExServer | Fl AutodiscoverServiceInternalUri
Get-OutlookAnywhere -Identity $ExServer\rpc (Default Web Site) |fl internalhostname

Hello

check all internal and external url:

Get-WebservicesVirtualDirectory -Server $ExServer |Fl internalURL,ExternalURL
Get-OWAVirtualDirectory -Server $ExServer | Fl internalUrl,ExternalURL
Get-ECPVirtualDirectory -Server $ExServer | Fl InternalURL,ExternalURL
Get-ActiveSyncVirtualDirectory -Server $ExServer | Fl InternalURL,ExternalURL
Get-OABVirtualDirectory -Server $ExServer | Fl InternalURL,ExternalURL
Get-ClientAccessServer $ExServer | Fl AutodiscoverServiceInternalUri
Get-OutlookAnywhere -Identity $ExServer\rpc (Default Web Site) |fl internalho

Hello

the "wrong" client trusted that certificate?

Hello

the "wrong" client trusted that certificate?

Hello

and all internal and external url have got value? or have got empty url?

What name(s) are listed in your certificate?? If you are using a wildcard you may need to request a duplicate which includes the CAS server name or the alias you are using for your Exchange environment.

My CAS and Exchange servers all use the same certificate, a wildcard, which list the domain.ext and *.domain.ext

I do not see any issues from Outlook, Activesync or OWA connections

What name(s) are listed in your certificate?? If you are using a wildcard you may need to request a duplicate which includes the CAS server name or the alias you are using for your Exchange environment.

My CAS and Exchange servers all use the same certificate, a wildcard, which list the domain.ext and *.domain.ext

I do not see any issues from Outlook, Activesync or OWA connections

Hi,

Please run the following command to check your certificate configuration in your Exchange server:

Get-ExchangeCertificate | fl

Please make sure the namespaces which are used for your service internal URLs and External Urls are included in your certificate and assigned with IIS service.

In client side, we can run the Test E-mail AutoConfiguration Tool to confirm whether the cas-1.dcc.local is used for any service URL:

Open Outlook - press CTRL key - right click on the Outlook icon from right bottom corner taskbar - Test Email AutoConfiguration. Put your email address - uncheck use guessmart and secure guessmart authentication - click Test to check your Autodiscover service.

Then check the Results tab and Log tab for service namespace.

Regards,