This is probably happening because it's coming upto your Exchange Server's 1 year anniversary. When Exchange 2007 first loads it installs it's own self-signed certificate but I believe this only lasts one year, the idea being that most people replace it with one from a Certification Authority which lasts for longer. Anyhow, you can simply create a new certificate! First open up the exchange shell and type the command Get-ExchangeCertificate | List This will show the current certificate and you can see the expiry date of it Create a new certificate with the command New-ExchangeCertificate It will prompt to overwrite SMTP, say Yes Now if you run Get-ExchangeCertificate | List You will see both certificates listed. They each have a thumbprint which is their unique identifier. You will also see that the old certificate is still being used for IIS. Enable the new certificate for IIS with the command Enable-ExchangeCertificate -Thumbprint (new certificate's thumprint) -Service IIS Now remove the old certificate Remove-ExchangeCertificate -Thumbprint (old certificate's thumbprint) And you're done

This is probably happening because it's coming upto your Exchange Server's 1 year anniversary. When Exchange 2007 first loads it installs it's own self-signed certificate but I believe this only lasts one year, the idea being that most people replace it with one from a Certification Authority which lasts for longer. Anyhow, you can simply create a new certificate! First open up the exchange shell and type the command Get-ExchangeCertificate | List This will show the current certificate and you can see the expiry date of it Create a new certificate with the command New-ExchangeCertificate It will prompt to overwrite SMTP, say Yes Now if you run Get-ExchangeCertificate | List You will see both certificates listed. They each have a thumbprint which is their unique identifier. You will also see that the old certificate is still being used for IIS. Enable the new certificate for IIS with the command Enable-ExchangeCertificate -Thumbprint (new certificate's thumprint) -Service IIS Now remove the old certificate Remove-ExchangeCertificate -Thumbprint (old certificate's thumbprint) And you're done