Ran into an issue recently where Outlook was working fine, however Android devices, particularly mobile phones, would throw an error that the certificate was invalid when configuring an Exchange mailbox via the GMail app. The error was:
Certificate not valid The Gmail app can't guarantee the security of this email address. Your messages would be at risk.
When clicking Advanced we received more clarification that the certificate was not trusted. However, we could quickly see that the correct certificate was being presented to the Android devices and it clearly wasn’t an issue with the date.
Certificate not trusted Contact your email provider about this error, or proceed with username (unsafe).
We then tested our certificate with DigiCert’s SSL Certificate Checker. This is a great tool to confirm that the certificate is installed correctly and that the certificate path is valid. You can check any certificate with this tool. It does not have to be a certificate issued by DigiCert. In our case we were testing our GoDaddy certificate with this tool. [Read more…] about GMail App fails to connect to Exchange – Certificate not valid