You may decrypt the conversation using a tool called "Network Monitor Decryption Expert" which is available for free from codeplex.
How do I go about decrypting the traffic?
Start Microsoft Network Monitor (NetMon) and capture the Traffic from Office 365. The latest version as of this writing is 3.4 which is available from http://www.microsoft.com/download/en/details.aspx?id=4865
Export the Server Certificate with private key in to a PFX
Install the Netmon expert for SSL
Now you should be able to decrypt the encrypted traffic.