We had an interesting issue this week. We renewed our Exchange certificate with a 3rd party vendor. Installed the certificate on Exchange and ISA Server. OWA access from the internet stopped working after we installed the certificates. We tested OWA internally and it worked which pointed to something on the ISA server. After a long investigation we found the issue to be ISA running on Windows 2003 which is not compatible with the Secure Hash Algorithm 2 (SHA2) family of hashing algorithms that the certificates from our 3rd party cert provider issues. Microsoft has a hotfix available to get around this. We were able to access OWA from the internet…