Interestingly, both the postal clause and and letters of marque are hold-overs from the (very few) powers granted by the articles of confederation. Without the power to tax or impose tariffs, I wonder to what degree the postal monopoly was seen as a revenue generating measure.
I believe you read the pirate bit wrong
> To define and punish Piracies and Felonies committed on the high Seas, and Offenses against the Law of Nations;
No, right below that: "[congress shall have the power] to declare War, *grant Letters of Marque and Reprisal*, and make Rules concerning Captures on Land and Water; "
Ah, fair enough. Technically, a privateer is not a pirate... but I'll grant that's only a technical distinction.
No—the constitution authorizes Congress “to establish post offices and post roads”. It does not obligate them to do so any more than it obligates them to declare war or hire pirates, to name two other clauses of the exact same section.