During your planning for SSL certificates for Exchange 2013 you may have chosen to use the same certificate on multiple servers.
The process for acquiring a certificate to be used on multiple servers is almost identical to the process for a single server. However during the Exchange 2013 certificate request wizard you would enter the fully qualified domain names of any additional Exchange servers that the SSL certificate will be used for.
For example in this certificate request the names for both servers E15MB1 and E15MB2 are being included in the certificate request.
After completing the certificate request you can then export the certificate and import it to additional servers with the following steps.
In the Exchange Administration Center navigate to Servers -> Certificates and choose the server that has the SSL certificate already installed.
Highlight the certificate to be exported, then click the “…” (more) icon and choose Export Exchange Certificate.
Enter a valid UNC path and the name of the file you wish to export to, and a password for the exported certificate.
Complete the export Exchange certificate wizard.
Open the “more” icon again and this time choose Import Exchange Certificate (it does not matter at this stage which server you have selected in the drop-down list above the icons).
Enter the UNC path to the file again, and the same password you used during the export.
Click the “+” icon and add any Exchange 2013 servers that you wish to import the certificate to.
Click Finish to complete the import wizard.
After you have imported the certificate to a server you can then proceed with assigning the SSL certificate to Exchange services.