Patent ID: 8799660

Claim:
A communication apparatus comprising: a first data storage; a second data storage; a third data storage for storing a particular certificate issued by a particular certificate authority; a printing device; a processor; and memory storing computer readable instructions, that cause, when executed by the processor, the communication apparatus to implement: receiving an electronic mail; storing the received electronic mail in the first data storage; executing a first verification, the first verification comprising determining whether a certificate attached to the received electronic mail matches the particular certificate stored in the third data storage; generating a first text digest from a text of the received electronic mail stored in the first data storage; generating a second text digest from an encrypted text of the received electronic mail; executing a second verification, the second verification comprising determining whether the first text digest matches the second text digest; controlling the printing device to print the received electronic mail when the first verification indicates verification successful and the second verification indicates verification successful; controlling the printing device to print the received electronic mail when the second verification indicates verification failed; deleting the received electronic mail from the first data storage in response to printing the received electronic mail; storing an address of a sender of the received electronic mail and its related mail information in the second data storage when the second verification indicates verification successful and when the first verification indicates verification failed, where the related mail information comprises the received electronic mail and a certificate of the received electronic mail; executing a third verification, the third verification comprising determining whether a certificate attached to a specific electronic mail in a specific mail information stored in the second data storage matches the particular certificate stored in the third data storage; and controlling the printing device to print the specific electronic mail when the third verification indicates verification successful.