Exchange issue

My FIM deployment is having problem with exchanging emails and I get this the following error logged in the event logs.

Microsoft.ResourceManagement.Service: System.ArgumentException: Invalid or NULL email address
   at Microsoft.ResourceManagement.Mail.Utilities.ValidateMailMessage(GenericMessage message, IMailServer mailServer)
   at Microsoft.ResourceManagement.Mail.NotificationMessage.Send(Int32 timeoutInMilliseconds)
   at Microsoft.ResourceManagement.Workflow.Hosting.SendMailWorkItemProcessor.SendMailMessage(MessageContent messageContent, Int32 timeoutInMilliseconds)
   at Microsoft.ResourceManagement.Workflow.Hosting.SendMailWorkItemProcessor.ProcessWorkItem(WorkItem workItem)

I got Exchange 2010. I logged in to each accounts (e.g. FIM Service account, FIM Admin account, test user accounts) using OWA and was able to send/receive emails w/o any issues; however, I do not see any emails in the service account mailbox, or for any users.

    <add key="mailServer" value="https://srv1.contoso.local/ews/exchange.asmx" />
    <add key="isExchange" value="1" />
    <add key="sendAsAddress" value="FimSvc@contoso.local" />
    <add key="synchronizationServerName" value="srv2.contoso.local" />

Any thoughts on what I should be looking into?

Thanks,
John