A communication apparatus includes: a first storage unit storing a certification authority certificate; a verification unit verifying an electronic signature attached to a first electronic mail received by a receiving unit from a mail server based on the certification authority certificate; an output unit outputting the first electronic mail when a verification result of the verification unit is positive; a deletion unit deleting the first electronic mail from the mail server; a notification unit notifying a user of information regarding a specific certification authority when a specific certification authority certificate is not stored in the first storage unit; an acquiring unit acquiring the specific certification authority certificate; and a storage control unit storing the acquired specific certification authority certificate. The receiving unit again receives the first electronic mail. The verification unit verifies an electronic signature attached to the again received first electronic mail based on the certification authority certificate.