[Oleg Krylov]

http://technet.microsoft.com/en-us/l...EXCHG.80).aspx
Раздел Limitations of the Self-Signed Certificate
Outlook Anywhere: The self-signed certificate cannot be used with Outlook Anywhere. We recommend that you obtain a certificate from a Windows PKI or a trusted commercial third party if you will be using Outlook Anywhere.

Там же:
Using the Self-Signed Certificate with Domain-Joined Outlook 2007 Clients
The self-signed certificate works without any additional configuration for domain-joined Microsoft Office Outlook 2007 clients.
Это относится только к внутренней сети.