At the moment, there is no way to connect your own USPS account to your Shippo account.
Shippo offers excellent discounted rates with USPS for domestic shipping within the United States. These rates are automatically activated in all Shippo accounts for all of our customers to take advantage of! Shippo’s discounts can save you up to 50% off of retail rates!
To get these kinds of rates, an individual business would have to be shipping over 50,000 packages with USPS per year, so we recommend giving our rates a try!