All the way back since the first Windows Mobile 2005-based devices started appearing on the market, I’ve had several questions from people who, for one reason or the other, couldn’t get their device to synchronize properly with an Exchange 2003 Server using Exchange ActiveSync (EAS). In most of the cases the reason turned out to be, that the mobile device simply didn’t trust the certificate provider, who issued the certificate that had been installed on the respective Exchange Server. For some reason (and I really don’t know why! ) a Windows Mobile 5 device, by default, doesn’t trust all the certificates Internet Explorer trusts. This means that you, in most situations, need to install the immediate and root certificates from the respective certificate provider manually on the device. This can typically be done by copying the certificate to the device (in .DER format), where you then simply double-click on it in File Explorer.
I’ll also include this information in one of my upcoming articles, that will cover the new Messaging Security Feature Pack (MSFP) also known as the Adaption Kit Update 2 (AKU2), which will appear here on MSExchange.org in a near future.