Echange Certificate expires

On SBS 2008, one year after the initial installation, your Exchange 2007 certificate will be expired.

Under Exchange Shell

Get-ExchangeCertificate | List

Locate the expired certificate and copy the footprint
Create a new certificate

New-ExchangeCertificate

Copy the new certificate thumbprint in order to activate it.

Enable-ExchangeCertificate -Thumbprint F7A8F1B443A0E7266C72CDE0603302C07B856076 -Service IIS

Then you can remove the old certificate.

Remove-ExchangeCertificate -Thumbprint 157700393E5D76615E855A773CFA08AB5842DFB0

After, you will need to install the new certificate to your computers. You can use GPO to do it.