Email disappearing cannot be a good thing!
Do you have a SMTP Connector for address space * that is configured to forward mail to the Yahoo server (as a smarthost)? Did you configure it to use SSL?
Here are some useful tools to troubleshoot such mailflow issues:
- Message Queues: Check the queues in ESM. Are messages still there?
- Message Tracking Logs: Track messages using the Message Tracking Center. Are messages making it to the Yahoo server?
- SMTP (protocol) logs: Check SMTP logs – these log details about SMTP sessions.
- Logging SMTP protocol activity
- Application Event Log: Check the Application Event Log for events from MSExchangeTransport.
- Diagnostics Logging: If you don’t find anything in the Application Event Log, bump up Diagnostics Logging (In SERVER-NAME -> Properties -> Diagnostics Logging tab) for MSExchangeTransport, and monitor the log events.