From BlackBerry KB Article #KB10571:
The subscriber was using the SIM card currently inserted in the BlackBerry device with another cell phone/device that had the Mobile Email application installed on it. The subscriber removed the SIM card and inserted it into the BlackBerry device without uninstalling Mobile Email from the previous device prior to transferring the SIM card to the BlackBerry device.
After transferring the SIM card to the BlackBerry device, the subscriber will begin to receive email messages that come from an unknown sender and a subject line of "Mobile Email". The contents of the message body contain "OZMAIL."
These email messages occur because the BlackBerry device cannot translate the email messages that are being sent from Mobile Mail. These email messages are also being directed to the SIM card.
Have the subscriber insert the SIM card back into the original cell phone and uninstall Mobile Email from the original device and transfer the SIM card back to the BlackBerry device.
If the subscriber is unable uninstall Mobile Email from the original device, the subscriber will have to change SIM cards.