My name is John and I'm a Guru here at Shopify!
While our integration with USPS does not currently manage pickups by the Post Office, they do have their own service to schedule a pickup you can look at.
It seems to only be available with certain mailing types on offer from them so check in with them directly on what kind of services you can use so they can pick up from you. :)
Best of luck with your store here and you can always reach out to us in Shopify support whenever you need a hand!
Has there been any update on this, or any ETA for it to be implemented? I just migrated from Etsy, where they just added the ability to schedule a pickup from USPS directly from your shop manager a few months ago, and it definitely made things way more convenient.
I know USPS has an API so I imagine it wouldn't be that difficult to implement. I wasn't able to find an app that adds the functionality either, but maybe I just missed something.