How to renew Microsoft Exchange Server Auth Certificate (Exchange 2016)

Hi @Sathishkumar Singh

An expired auth certificate will prevent you from accessing ECP and OWA, Outlook clients slow to start and not displaying the user's calendar and so on...

You could follow the steps below to renew your auth certificate, which is recorded in Microsoft official document: Can't sign in to Outlook on the web or EAC if Exchange Server OAuth certificate is expired

To check the status of your existing OAuth certificate, run the following command in the Exchange Management Shell:

(Get-AuthConfig).CurrentCertificateThumbprint | Get-ExchangeCertificate | Format-List  

1.Create a new OAuth certificate by running the following command:

New-ExchangeCertificate -KeySize 2048 -PrivateKeyExportable $true -SubjectName "cn=Microsoft Exchange Server Auth Certificate" -FriendlyName "Microsoft Exchange Server Auth Certificate" -DomainName @()  

2.Set the new certificate for server authentication. To do this, run the following commands:

Set-AuthConfig -NewCertificateThumbprint <ThumbprintFromStep1> -NewCertificateEffectiveDate (Get-Date)  
Set-AuthConfig -PublishCertificate  
Set-AuthConfig -ClearPreviousCertificate  

3.Restart the Microsoft Exchange Service Host Service.

4.Either run the IISReset command to restart IIS or run the following commands (in elevated mode) to recycle the Outlook on the web and EAC application pools:

Restart-WebAppPool MSExchangeOWAAppPool  
Restart-WebAppPool MSExchangeECPAppPool  

If you want to refer to a link with step-by-step screenshot, this link will be helpful as well:
Resolve the ‘Auth Certificate Missing’ Error in Exchange 2016/2013
Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

In addition, it may take several hours for the renewed certificate to take effect, please wait patiently.

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https://learn.microsoft.com/en-us/exchange/plan-and-deploy/integration-with-sharepoint-and-skype/maintain-oauth-certificate?view=exchserver-2019