N8 has Mail for Exchange email account (using Gmail) created and there are some messages with attachments.
Invoking QMessageService::retrieve() for QMessageId that represents a message with attachement and QMessageContentContainerId that represents this attachement returns true but no QMessageService::stateChanged(QMessageService::State) is emitted and in logs following message is printed few times:
ERROR - Capability check failed - A Message (function number=0xffffffff) from Thread neasserver.exe[20012be6]0001::JavaCommsClient-10000-0x01617610-130060903, sent to Server java-comms-10000, was checked by Thread javacaptain.exe[200211dc]0001::JavaCommsServer-10000-0x00701e00-16807 and was found to be missing the capability: TrustedUI. Additional diagnostic message: javacomms: install application not allowed

Capability check failed should not be printed as this indicates that binary (i.e. neasserver.exe) used internally by Qt Messaging is invoked with insufficient capabilities. Signal stateChanged() should be emitted after some time (i.e. after receiving operation somehow finishes).

Test code attached.