Thanks for your feedback here, but I cannot see the benefits of such a quarantine - maybe you can go into details about such a configuration.
Outgoing: if a message is too big, the internal mail server shoult reject it and the user knows immediately that it does not work and he has to send a smaller one. moving the message to a quarantine make no sense for me.?
incoming: if a message is addressed to an valid user, why do you NOT want to give him the message directly, why do you want to quarantine?