Communication apparatus

A communication apparatus that is connectable to a mail server, the communication apparatus comprising:

• a receiving unit that is configured to receive electronic mail from the mail server;
• a first storage unit that is configured to store a certification authority certificate;
• a verification unit that is configured to verify an electronic signature attached to a first electronic mail received by the receiving unit based on the certification authority certificate stored in the first storage unit;
• an output unit that is configured to output the first electronic mail when a verification result of the verification unit is positive;
• a deletion unit that is configured to delete the first electronic mail from the mail server when the first electronic mail is configured to be output by the output unit;
• a notification unit that is configured to notify a user of information regarding a specific certification authority when a specific certification authority certificate is not stored in the first storage unit, wherein the specific certification authority certificate is issued by the specific certification authority that authenticates the electronic signature attached to the first electronic mail received by the receiving unit;
• an acquiring unit that is configured to acquire the specific certification authority certificate in accordance with an operation by the user;
• and
• a storage control unit that is configured to store the specific certification authority certificate acquired by the acquiring unit in the first storage unit,
• wherein the receiving unit again receives the first electronic mail from the mail server when the mail server stores the first electronic mail, and
• wherein the verification unit verifies an electronic signature attached to the again received first electronic mail based on the certification authority certificate stored in the first storage unit.