Error 5016 exchange free busy,  Can't  see free busy of other calendars






  1. First Reason: Certificate is not assigned appropriately to the Exchange services such smtp/IIS.
  2. Second Reason could be the Federated Trust between on-Premise and Exchange Online.

To use this feature several things will need to be configured:

  • trust with the Microsoft Federation Gateway.
  • organizational relationship must be configured.
  • autodiscover and EWS must allow WS Security authentication.

The proxy needs to allow unauthenticated traffic to the following url’s:

  • /EWS/exchange.asmx/WSSecurity.
  • /autodiscover/autodiscover.svc/WSSecurity.
  • /autodiscover/autodiscover.svc.


So we need to :

  • verify if autodiscover allows WS Security for authentication
  • verify the external EWS url
  • verify if Exchange Web Services will allow WS Security for authentication





Solution 1: Verify Certificate

Import the certificate

Import-ExchangeCertificate -Path C:\CertificateFile.crt

Enable-ExchangeCertificate -Thumbprint paste_thumbprint_here -Services "SMTP, IMAP, IIS"




Solution 2: Verify AutodiscoverVirtualDirectory


Get-AutodiscoverVirtualDirectory|select server, WSSecurityAuthentication


Verify if the value of the column WSSecurityAuthentication is set to true


Get-AutodiscoverVirtualDirectory|Set-AutodiscoverVirtualDirectory -WSSecurityAuthentication:$true


Using this cmdlet the authentication method will be configured but to offer this authentication type you will need to perform an IISReset. Additional you can verify if the svc-integrated handler is attached to the autodiscover virtual directory:



Solution 3:Verify the Exchange Web Services


this can be done by using the Get-WebServicesVirtualDirectory cmdlet:

Get-WebServicesVirtualDirectory|select server, ExternalUrl, WSSecurityAuthenticationcmdle


WSSecurityAuthentication needs to be set to tru

In case that WSSecurity is not true enabled it by using the following cmdlet:

Get-WebServicesVirtualDirectory|Set-WebServicesVirtualDirectory -WSSecurityAuthentication:$true


If no external url is configured you will need to configure one


To verify if the certificate contains the correct names we will use Powershell again:

Get-ExchangeCertificate|? {$_.Services -like “*IIS*”}|select Subject, CertificateDomains|FL

Verify if the CertificateDomains contain the FQDN you are planning to use for EWS, for of If this name is not on the certificate you will need to renew your certificate.


Get-WebServicerVirtualDirectory|Set-WebServicesVirtualDirectory -Externalurl “


Solution 4: verify the Federation Trust


This can be done by starting with Test-FederationTrustCertificate which will verify if the certificate used for the trust is correct and is installed on all CAS




Test-FederationTrust cmdlet to verify if the Federation Trust really works




Test-FederationTrust -UserIdentity


I also imported all the federation certificate in the new exchange server after exporting it from the old server


Solution 5:  verify the Organization Relationship


 not all domains are listed here it can cause strange issues such as it works for domain.


Make sure you add your to the organizational sharing domains


Get-OrganizationRelationShip,  retrieves the current configuration

GetFederationInformation, will send an autodiscover request to the other organization to retrieve the configuration


The following parameters are important in this case:




Solution 6: OU

Makesure that the users is in the OU that is synced with o365


Solution 7: Autodiscover


Check that the autodiscover URL  ( ) is accessible internally and externally. If it is not accessible, check the authentication and  change the authentication for the autodiscover in IIS if it is needed.


 -WindowsAuthentication $false

-BasicAuthentication $false

-DigestAuthentication $true


Solution 8: Run the Hybrid Configuration Wizard


Run  the latest version of HCW on Exchange 2013.


Solution 8: Set-IntraOrganizationConnector


Set-IntraOrganizationConnector "MainCloudConnector" -Enabled $false



How to troubleshoot free/busy issues in a hybrid deployment of on-premises Exchange Server and Exchange Online in o365

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