Exchange Edge is using self-signed certificate for the SMTP services and for subscribe new Exchange synchronization between Hub and Edge servers.
Self-signed certificates are only valid for one year.
To display certificate used by Exchange Server run this command:
Get-ExchangeCertificate | fl
To renew a self-signed certificate for Exchange Edge you can use Exchange Management Shell command:
Get-ExchangeCertificate | New-ExchangeCertificate
To [...]

How to uninstall Mailbox Role on Exchange Server 2007?

Run commend: setup /m:uninstall /r:mailbox
?

How to view Exchange installed certificates in exchange management shell?
Simple run Exchange Management Shell an run the command: Get-ExchangeCertificate | fl

Verb: Services inform you with services use this certificate.
In my example this is IMAP, POP, IIS and SMTP services.

Useful links:

New-ExchangeCertificate cmdlet on Microsoft Technet: http://technet.microsoft.com/en-us/library/aa998327.aspx
Get-ExchangeCertificate cmdlet on Microsoft Technet: http://technet.microsoft.com/en-us/library/bb124950.aspx
Import-ExchangeCertificate cmdlet on Microsoft Technet: http://technet.microsoft.com/en-us/library/bb124424.aspx

 
We need certificates to publish internal Exchange 2007 services (like OWA, ActiveSync, OutlookAnywhere) using Microsoft ISA 2006. We want to get a private SLL certificate from internal Certification Authority (CA). We have to generate a certificate request, for example [...]