Exchagne Web Services - The Autodiscover service couldn't be located

Question

I have a Exchange 2013 server (Windows Server 2013). Single server with all roles Domain controller, AD, Exchange server etc. Now I am writing basic Exchange web services sample code. Below is the code I am trying. If run this code on Exchange server itself, test email gets sent. But if I run same code on another Windows 10 machine in same domain, it does not works. It gives exception below.

On Windows10 machine I have set DNS IP to point Windows Server 2013(Exchange server), with that I can ping to example.com. What I am missing here, why this code is not working on Windows 10 machine in same domain.

Also did not understand why, it is looking for http://autodiscover.example.com. This is not I have defined anywhere.

    static void Main(string[] args)
    {
        ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
        service.Credentials = new WebCredentials("User2001@example.com", "Pass@123");
        service.TraceEnabled = true;
        service.TraceFlags = TraceFlags.All;
        service.AutodiscoverUrl("User2001@example.com", RedirectionUrlValidationCallback);

        EmailMessage email = new EmailMessage(service);
        email.ToRecipients.Add("User2002@example.com");
        email.Subject = "HelloWorld";
        email.Body = new MessageBody("This is the first email I've sent by using the EWS Managed API");
        email.Send();
    }

    private static bool RedirectionUrlValidationCallback(string redirectionUrl)
    {
       return true;
    }

    Unhandled Exception: Microsoft.Exchange.WebServices.Data.AutodiscoverLocalException: The Autodiscover service couldn't be located.
   at Microsoft.Exchange.WebServices.Autodiscover.AutodiscoverService.InternalGetLegacyUserSettings[TSettings](String emailAddress, List`1 redirectionEmailAddresses, Int32& currentHop)
   at Microsoft.Exchange.WebServices.Autodiscover.AutodiscoverService.GetLegacyUserSettings[TSettings](String emailAddress)
   at Microsoft.Exchange.WebServices.Autodiscover.AutodiscoverService.InternalGetLegacyUserSettings(String emailAddress, List`1 requestedSettings)
   at Microsoft.Exchange.WebServices.Autodiscover.AutodiscoverService.GetUserSettings(String userSmtpAddress, UserSettingName[] userSettingNames)
   at Microsoft.Exchange.WebServices.Data.ExchangeService.GetAutodiscoverUrl(String emailAddress, ExchangeVersion requestedServerVersion, AutodiscoverRedirectionUrlValidationCallback validateRedirectionUrlCallback)
   at Microsoft.Exchange.WebServices.Data.ExchangeService.AutodiscoverUrl(String emailAddress, AutodiscoverRedirectionUrlValidationCallback validateRedirectionUrlCallback)
   at EWSTest.Program.Main(String[] args) in c:\users\administrator\source\repos\EWSTest\EWSTest\Program.cs:line 18


    
    Starting SCP lookup for domainName='example.com', root path=''
    
    
    Searching for SCP entries in LDAP://CN=Configuration,DC=example,DC=com
    
    
    Scanning for SCP pointers Domain=example.com
    
    
    No SCP pointers found for 'Domain=example.com' in configPath='CN=Configuration,DC=example,DC=com'
    
    
    Scanning for SCP urls for the current computer Site=Default-First-Site-Name
    
    
    Adding (prio 1) 'https://NileshWin12Excg.example.com/Autodiscover/Autodiscover.xml' for the 'Site=Default-First-Site-Name' from 'LDAP://CN=NILESHWIN12EXCG,CN=Autodiscover,CN=Protocols,CN=NILESHWIN12EXCG,CN=Servers,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative Groups,CN=exampleOrg,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=example,DC=com' to the top of the list (exact match)
    
    
    Trying to call Autodiscover for User2001@example.com on https://nileshwin12excg.example.com/Autodiscover/Autodiscover.xml.
    
    
    POST /Autodiscover/Autodiscover.xml HTTP/1.1
    Content-Type: text/xml; charset=utf-8
    Accept: text/xml
    User-Agent: ExchangeServicesClient/15.00.0913.015


    
    
      
        
          User2001@example.com
          http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a
        
      
    
    
     failed: WebException (The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.)
    
    
    Trying to call Autodiscover for User2001@example.com on https://example.com/autodiscover/autodiscover.xml.
    
    
    POST /autodiscover/autodiscover.xml HTTP/1.1
    Content-Type: text/xml; charset=utf-8
    Accept: text/xml
    User-Agent: ExchangeServicesClient/15.00.0913.015


    
    
      
        
          User2001@example.com
          http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a
        
      
    
    
     failed: WebException (The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.)
    
    
    Trying to call Autodiscover for User2001@example.com on https://autodiscover.example.com/autodiscover/autodiscover.xml.
    
    
    POST /autodiscover/autodiscover.xml HTTP/1.1
    Content-Type: text/xml; charset=utf-8
    Accept: text/xml
    User-Agent: ExchangeServicesClient/15.00.0913.015


    
    
     failed: WebException (The remote name could not be resolved: 'autodiscover.example.com')
    
    
    Trying to get Autodiscover redirection URL from http://autodiscover.example.com/autodiscover/autodiscover.xml.
    
    
    Request error: The remote name could not be resolved: 'autodiscover.example.com'
    
    
    No Autodiscover redirection URL was returned.
    
    
    Trying to get Autodiscover host from DNS SRV record for example.com.
    
    
    DnsQuery returned error error 'DNS name does not exist' error code 0x0000232B.
    
    
    No appropriate SRV record was found.
    
    
    No matching Autodiscover DNS SRV records were found.

Xavier · Accepted Answer

Looks like you having secure connection issues;

Process

Client sends LDAP query to the AD
AD returns a list of SCP points
Client attempts to connect to the returned points
If a valid response comes back, happy days.

In your case the server is returning

https://nileshwin12excg.example.com/Autodiscover/Autodiscover.xml - Result : failed: WebException (The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.)

https://example.com/autodiscover/autodiscover.xml - Result : failed: WebException (The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.)

http://autodiscover.example.com/autodiscover/autodiscover.xml - Result : Request error: The remote name could not be resolved: 'autodiscover.example.com'

So it would seem that the client can not establish a trusted connection to https://nileshwin12excg.example.com or https://example.com/, try to get to these URLs from the machine where you are having trouble. It may be you are using self-signed certs for your web services that are not trusted on the client machine.

EDIT

Add

ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) => true;

To your startup to tell you application to always accept the server certificate as valid.

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