That’s where the Skald’s Mail – A Courier Alternative mod comes in. It lets you rent or purchase a mailbox and use it to collect all the letters a courier might otherwise hand-deliver to you. That should make the flood of letters you get in the early levels a bit less annoying, but if you need to hear the custom dialog that comes with some of the bigger deliveries, you still have the option to receive those by hand.
These custom mailboxes also let you do mail order shopping by picking up catalogues from shops around the world. Similarly, you can send off weapons and armour for improvement at Warmaiden’s, or bows and arrows to the Fletcher in Solitude.