- Open Exchange Management Console > navigate to Server Configuration and review the Certificates in the right panel
- Identify the certificate that has expired (take note of the subject name and the services)
- Start ExMngmtnShell as Administrator
- type Get-ExchangeCertificate to list the installed certificates
- Match the certificate to the expired certificate (using subject the name and services) from the Console then copy the associated thumbprint
- Type Get-ExchangeCertificate –Thumbprint INSERTTHUMBPRINTHERE | New-ExchangeCertificate
- Remove the old expired certificate either from the Console or from the Shell using Remove-ExchangeCertificate -Thumbprint INSERTTHUMBPRINTHERE
Note: I had to restart the server for the certificate to take effect.