An mail processing apparatus for confirming contents of encrypt mail. Electronic mail delivered in MTA is received by a receiving section. When the received electronic mail has been encrypted or an electronic signature has been affixed, signature verification and decoding are performed by an electronic signature verification/decoding section. The contents of the mail in which the signature verification and the decoding are performed are confirmed by a content confirmation section. Subsequent to this, a signature and encryption are properly performed with respect to the mail by an electronic signature/encryption section. Mail of an account destination of a mail server is held in a spool. The spooled mail is taken out using a delivery part by a mail user agent device. Mail of an account destination of another mail server is delivered to another mail server destination through the delivery section.