First, copy the Intermediate certificate from the email you received and then follow these simple instructions:

• Copy the intermediate certificate from the body of the email and paste it into a simple text editor of your choice, such as Notepad.
• Save it as intermediate.cer on your desktop.
• Open MMC.
• Select File, Add/Remove Snap In.
• Select Add.
• Select Certificates, Add.
• Select Computer Account, Next.
• Local Computer, Finish, Close, OK.
• Select Certificates, Intermediate Certification Authorities, Certificates.
• Right-Click Certificates, All-Tasks, Import.

The Import Wizard should now start. Next, just follow the instructions to import the intermediate certificate and close MMC.

Copy the SSL certificate from the email and then save this as mydomain.cer to whichever location you want.

Next, open the Exchange Management Shell and run the import and enable commands together separated by a pipe character:

Import-ExchangeCertificate -Path C:\mydomain.cer | Enable-ExchangeCertificate -Services "SMTP, IMAP, POP, IIS"

The services can be any combination of these values: IMAP, POP, UM, IIS, SMTP.

You can verify that your certificate is enabled and running by using the following command:

Get-ExchangeCertificate -DomainName mydomain.cer

In response to the above command you should see the certificates thumbprint, an abbreviated list of the services and mydomain.cer. You can re-run the modified Enable command with the certificate thumbprint if your certificate isn’t enabled correctly.

Enable-ExchangeCertificate -Thumbprint [paste thumbprint here] -Services "SMTP,IMAP, POP, IIS"

Finally, reboot your server and then test your certificate is working properly by connecting with IE, ActiveSync or Outlook.