Renew a Certificate in Exchange 2016 & 2019

How to renew a certificate in Exchange

In this article, we explore the process of renewing a third-party certificate in Exchange 2016 CU23 and greater and Exchange 2019 CU12 and greater. This process differs from the older cumulative updates (and Exchange 2013), where it was still possible to renew a third-party certificate through the Exchange Admin Center (GUI).

If you are still on Exchange 2013, or older versions of Exchange 2016 or Exchange 2019, consider using this article instead for the Exchange Admin Center method.

Note: It is still possible to use the Exchange Admin Center to generate and renew self-signed certificates. Self-signed certificates are out of the scope of this article.

In this article, we demonstrate how to accomplish this using the PowerShell commands. The high-level steps include:

• Create a new certificate signing request
• Upload the certificate signing request to your certificate provider
• Download the processed certificate from your certificate provider
• Install the certificate on Exchange
• Assign Exchange services to the new certificate on each server
• Delete the old certificate
• Export the new certificate to a PFX file
• Import the certificate to all other Exchange servers

Let’s get started!

Renew a Certificate with PowerShell

As mentioned earlier, newer versions of Exchange 2016 and Exchange 2019 require that third-party certificate requests be conducted through PowerShell. Third-party certificate requests can no longer be requested or renewed through the Exchange Admin Center.

To start, launch the Exchange Management Shell (either from the Exchange Server or a workstation that has the Exchange Management Tools installed).

First, we need to find the thumbprint of the certificate we plan to renew. To do this, we can run the Get-ExchangeCertificate command and filter the responses to only certificates that are issued by a third-party certificate authority.

 C:\> Get-ExchangeCertificate | Where {$_.IsSelfSigned -eq $false} | Format-List FriendlyName, CertificateDomains, Thumbprint, NotAfter

This will return all certificates that are not self-signed. In our example, we see just a single certificate returned. This certificate is named mail.exchangeservergeek.com and has a corresponding thumbprint. This is the certificate we will be renewing.

FriendlyName : mail.exchangeservergeek.com
CertificateDomains : {mail.exchangeservergeek.com, autodiscover.exchangeservergeek.com}
Thumbprint : B26C3C9B30A2A7371767275043816466CB921738
NotAfter : 7/15/2023 12:00:00 AM

Now that we have the thumbprint let’s renew the certificate. To do this, we will pipe the thumbprint using the Get-ExchangeCertificate command into the New-ExchangeCertificate command. We will then save the output of New-ExchangeCertificate into a variable named $certrequest.

 C:\> $certrequest = Get-ExchangeCertificate -Thumbprint B26C3C9B30A2A7371767275043816466CB921738 | New-ExchangeCertificate -GenerateRequest -PrivateKeyExportable:$true

The example above is leveraging the following parameters:

• Thumbprint identifies the certificate we plan to renew.
• GenerateRequest is used to generate a certificate request for a third-party certificate authority. Without this parameter, you would generate a self-signed certificate issued by the Exchange Server.
• PrivateKeyExportable allows you to copy this certificate to other Exchange Servers. If you have more than one Exchange Server, you need this parameter set to $true. If you omit this parameter (or set it to $false), you can only use this certificate on the Exchange Server that generated the certificate request.

Now that we have the Exchange certificate stored in a variable, we need to get that variable saved into a file. To do that, run the following command.

 C:\> [System.IO.File]::WriteAllBytes('\\EX19-01\C$\Users\<user>\Desktop\certrequest.txt', [System.Text.Encoding]::Unicode.GetBytes($certrequest))

In this command, two things are important. First, you must specify a UNC path to where you want to save the certificate request file. In our example, we saved this to our desktop as a text file named certrequest.txt. The second is what we are exporting into that file. In this case, it is the contents of the variable $certrequest. As soon as you run this command, the file will be created in the location specified.

By running the following command, you will notice we have two certificates with the name mail.exchangeservergeek.com; however, one of these will be in a Pending Request state. The duplicate minimizes downtime for your users because it allows you to process the certificate renewal without affecting the existing certificate.

 C:\> Get-ExchangeCertificate | Format-Table Subject, Status

Subject                                                 Status
-------                                                 ------
CN=mail.exchangeservergeek.com                  PendingRequest
CN=mail.exchangeservergeek.com                           Valid
CN=EX19-01                                               Valid
CN=Microsoft Exchange Server Auth Certificate            Valid
CN=WMSvc-SHA2-EX19-01                                    Valid

Processing a certificate request

Before we can use our certificate, we must process this request through a third-party certificate provider. There are plenty out there, but I personally recommend DigiCert (affiliate). Not only do they have fantastic technical support, but they also have some really neat certificate tools. Best of all, their certificate turnaround time is incredibly fast (even on a Sunday at 7:42 pm–yep, personal experience right there.).

The specific steps for each certificate provider are different, but the principles remain the same. You provide a certificate request. The provider validates your identity. The provider then issues you a certificate.

First, we need to get the certificate request we created in the previous section. This should have created a file on your desktop (or the path you specified). Open this file with Notepad and copy the entire contents, including the BEGIN and END lines.

Next, we need a Unified Communications (UC) certificate. This is also referred to as a Subject Alternative Name (SAN) certificate. As mentioned above, I recommend DigiCert (affiliate).

At some point, the 3rd party certificate authority will ask you to paste the contents of the CSR file into their system for processing. From this file, the provider will identify all the subject and alternate names you need. Using our previous example, the certificate provider identified we requested both mail.exchangeservergeek.com and autodiscover.exchangeservergeek.com. The validation process will then begin.

Note: Some certificate providers allow you to prepay for several years in advance but will only issue a certificate for a single year. In those instances, you may need to rekey the existing certificate and then provide the CSR to the provider.

The validation process can vary between providers as well. Some providers will perform a simple domain validation where they send an email to the recipients listed on your domain registration. Others will perform more extensive checks, including the validation of your business against various agencies.

Once your identity has been validated and your certificate approved, download and unpack your certificate. Often providers will ask you what system the certificate is for. If you have the option for Exchange, this will give you the appropriate certificate bundle. You will then be ready to complete your certificate request.

Complete the certificate renewal with PowerShell

To complete our pending certificate, we need to leverage the Import-ExchangeCertificate command. In our example below, the Import-ExchangeCertificate command is leveraging the following parameters.

 C:\> Import-ExchangeCertificate -FriendlyName mail.exchangeservergeek.com -FileData ([System.IO.File]::ReadAllBytes('\\EX19-01\C$\Users\<user>\Desktop\mail_exchangeservergeek_com.cer')) -PrivateKeyExportable $true

• FriendlyName is purely for display. It identifies how you want the certificate to appear in the Exchange Admin Center and PowerShell. It is beneficial to put something descriptive in this field. If you omit this field, Exchange names the certificate “Microsoft Exchange”. In our example above, we made the friendly name the same as the subject name.
• FileData is the UNC path to the certificate we downloaded from the certificate authority. In our example, we saved the file mail_exchangeservergeek_com.cer to our desktop for easy access.
• PrivateKeyExportable allows you to copy this certificate to other Exchange Servers. If you have more than one Exchange Server, you need this parameter set to $true. If you omit this parameter (or set it to $false), you can only use this certificate on the Exchange Server that generated the certificate request.

Assign Services to a Certificate with PowerShell

To assign services using PowerShell, we will need to capture the thumbprint of our new certificate. To do this, we will need to first run the Get-ExchangeCertficate command.

 C:\> Get-ExchangeCertificate | Format-Table Subject, Thumbprint, NotAfter

Subject                          Thumbprint                               NotAfter
-------                          ----------                               --------
CN=mail.exchangeservergeek.com   BD09E758DF572307128D878697D3A766BDBEBF35 7/15/2024
CN=mail.exchangeservergeek.com   B26C3C9B30A2A7371767275043816466CB921738 7/15/2023
CN=EX19-01                       C232F4D642F74B9DC7E4ED33D4AB56E68C10CA76 1/1/2028
CN=Microsoft Exchange Server...  411A27BA64FD140523E4D1CF088589C228CA9C5E 12/4/2027
CN=WMSvc-SHA2-EX19-01            D894B092E2ABE925E7104A0C9DFF6C448182CA30 12/27/2032

You will notice we have a duplicate of the certificate. The one with the later expiration date (NotAfter column) is your new certificate. In our example above, the thumbprint highlighted in green, with the NotAfter date of 7/15/2024, is our new certificate. The thumbprint highlighted in blue, with the NotAfter date of 7/15/2023, is our current certificate that users are still leveraging.

This new certificate is not yet live. To make it live, we must assign services to the certificate. To do this, we run the following command. Be sure to use the new thumbprint.

Note: When you assign services to a certificate, it will impact current connections to Exchange. For example, assigning IIS to a certificate can cause Outlook clients to reconnect. You may wish to perform this action during a maintenance window or after hours.

 C:\> Enable-ExchangeCertificate -Server EX19-01 –Thumbprint BD09E758DF572307128D878697D3A766BDBEBF35 –Services IIS,SMTP

In this command:

• Server specifies which server you want the action performed against. If you omit this parameter, the action is performed against the server where PowerShell is connected.
• Thumbprint specifies the certificate to configure via its thumbprint
• Services define which components you want to use the certificate with (e.g. IIS, SMTP, POP, IMAP, etc.)

If you specified SMTP as a service to add to the new certificate, you will be prompted on whether to overwrite the existing default SMTP certificate. Enter Y and press Enter.

Overwrite the existing default SMTP certificate?
Current certificate: 'B26C3C9B30A2A7371767275043816466CB921738'
Replace it with certificate: 'BD09E758DF572307128D878697D3A766BDBEBF35'
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [?] Help (default is Y): Y

In our example, we enabled IIS and SMTP for our renewed certificate. Let’s see how things look by running a slightly different Get-ExchangeCertificate command.

 C:\> Get-ExchangeCertificate | where {$_.IsSelfSigned -eq $false} | Format-List FriendlyName,Thumbprint,NotAfter,Services

FriendlyName : mail.exchangeservergeek.com
Thumbprint : BD09E758DF572307128D878697D3A766BDBEBF35
NotAfter : 7/15/2024 12:00:00 AM
Services : IIS, SMTP

FriendlyName : mail.exchangeservergeek.com
Thumbprint : B26C3C9B30A2A7371767275043816466CB921738
NotAfter : 7/15/2023 12:00:00 AM
Services : None

The green thumbprint, with a NotAfter date of 7/15/2024, identifies our new certificate. The blue thumbprint, with a NotAfter date of 7/15/2023, identifies the old certificate that is about to expire. Now that we have successfully assigned services to our new certificate let’s make sure it is working as expected.

Checking your work

Now that we have our new certificate installed, we need to test it to make sure it is working properly.

The easiest way to check is to enter your URL into a web browser. In our case, we enter https://mail.exchangeservergeek.com/ecp. This should result in no certificate errors. You can also select the padlock in the address bar and explore the properties of the certificate to verify the updated expiration date and certificate chain.

DigiCert’s SSL Certificate Checker is a great tool to confirm that the certificate is installed correctly and that all intermediary certificates in the chain are valid. You can check any certificate with this tool. It does not have to be a certificate purchased from DigiCert. 

Test results all good? Awesome! Your certificate is correctly installed.

If you have Exchange Hybrid

If you have Exchange Hybrid, it is highly likely your old certificate is being used for hybrid mail flow (forced TLS) between Exchange Online and Exchange on-premises.

If you are running Exchange Hybrid, rerun the Hybrid Configuration Wizard and select your new certificate to be used for hybrid mail flow. When the hybrid configuration wizard completes, you will be able to delete the old certificate from Exchange.

Delete the old certificate with PowerShell

Now that everything is correctly installed, we can delete the old certificate. To delete your old certificate, run the following command, specifying the old thumbprint. Hit Enter to confirm.

Note: I would recommend delaying the deletion of the old certificate for a few days just in case you need to roll back your changes.

 C:\> Remove-ExchangeCertificate -Server EX19-01 -Thumbprint B26C3C9B30A2A7371767275043816466CB921738 
Confirm 
Are you sure you want to perform this action? 
Remove certificate with thumbprint B26C3C9B30A2A7371767275043816466CB921738 from the computer's certificate store? 
[Y] Yes [A] Yes to All [N] No [L] No to All [?] Help (default is "Y"):

The old certificate will be removed. To confirm removal, rerun the Get-ExchangeCertificate cmdlet above.

More than one server?

If you have multiple Exchange servers, you will also need to copy this certificate to each Exchange Server. To do this, check our article on importing and exporting Exchange certificates. If you have a load balancer in the mix, you will need to copy the certificate to that device as well.

Further Reading

Here are some articles I thought you might like.

• Generate a Certificate Request for Exchange 2016 and Exchange 2019
• Complete a Certificate Request for 2016 and Exchange 2019
• Assign Services to a Certificate for Exchange 2016 and Exchange 2019
• Import & Export SSL Certificates in Exchange 2016 and Exchange 2019
• Generate a Certificate Request for Exchange 2013
• Complete a Certificate Request in Exchange 2013
• Assign Services to a Certificate in Exchange 2013
• Import & Export a Certificate in Exchange 2013
• Renew a Certificate in Exchange 2013