mdc

assuming that a sender has signed and encrypted a message,

how does using MDC protect the sender/recipient more than the signing and
encrypting of the message?

what tampering can be done with the message that the recipient would not
detect unless mdc were used?

{have read rfc-2440 bis, sections 5.12 and 5.13, but did not understand the
practical security advantages
over signing and encrypting}

tia for any clarifications,

vedaal