PostGrid has been great for automating our insurance mails for our client
USPS Informed Delivery - Get an image of your mail before it arrives
Lob - A simple API to integrate print & mail solutions into your applications.
PackageX - PackageX is a modern logistics platform.
Postalytics - Automated direct mail software that’s faster, smarter & better. Postalytics sends personalized direct mail from your CRM and analyzes delivery & response.
Shippo Package Tracking API - One API to track packages across multiple shipping carriers
AmazingMail - Business print-mail solution