A memory section of a server apparatus stores a security information table storing a plurality of pieces of destination management information, a trust information table storing a plurality of pieces of source management information, and a message information table storing a plurality of pieces of message information. A control section of the server apparatus, when it receives data, and if a piece of changed destination identification information is included in first destination management information that corresponds to destination data in the data, transmits a first message that depends on a trust level included in first source management information that corresponds to the source data in the data.