Exchange

TLS certificate expired, Exchange showing invalid internal SMTP certificate for the FQDN.  resolved by going to the Exchange Shell.

http://blog.bruteforcetech.com/archives/708

using the following:

Enable-ExchangeCertificate (either by itself or with the switches and values).

Enable-ExchangeCertificate -thumbprint {value} -services {smtp}  (no brackets needed for the values)

Cert expires in 2013