Sure, the ISP _should_ deliver the packets. No worries.

The user agent should... be an agent for the user, and be able to perform actions on their behalf.

(The legality of those actions is of course assumed by the user here... if I add an automated flamethrower to my mailbox and burn my bills, well the debt collectors may come regardless if I read them or not - we cannot shift blame to the USPS here).