While a large portion of the labels generated in ShipStation are shipped via the USPS, ShipStation doesn't offer a direct integration to a USPS account. Instead, ShipStation offers a complimentary integration with USPS label provider Stamps.com and this is available to all US-based ShipStation accounts. Following the steps below, you'll be able to create your very own complimentary Stamps.com account within ShipStation (You're also more than welcome to connect an existing Stamps.com account to ShipStation. It will convert to a complimentary "ShipStation Pro Plan $0" on your next month's Stamps.com billing cycle).
Head to the Carrier Management section of your ShipEngine account.
At the bottom of the page, select the UNITED STATES POSTAL SERVICE BY STAMPS.COM box in the upper lefthand side.
Click the green Connect button in the lower righthand side of the popup, and continue to the Get Started page.
Now, fill out the info on the Create Your Stamps.com Account page. (If this is an existing account that you would like to add, click I already have a Stamps.com account and enter in your username and password.)
Once you've filled this out, click Create Free Account and you'll be able to ship with the USPS!
For more information on what this Stamps.com account will offer, check out our Stamps.com partner page!