We use Lob to handle our physical mail programmatically. Instead of dealing with printers, postage, and manual mailing, we send the request through their API and Lob takes care of the print and delivery side.
It's become the piece we don't have to think about anymore. We generate the documents on our end, hand them off, and they go out reliably. That's exactly what we wanted from it. The API integration is seamless. Review collected by and hosted on G2.com.
Honestly, not much. If I had to name something, there was a bit of a learning curve early on getting everything dialed in the way we wanted. Once it was set up, though, it just ran. Review collected by and hosted on G2.com.