The Postmark and Zapier integration has been updated to support Message Streams, allowing users to specify which stream they'd like to send their email through when triggering emails via Zapier. This feature provides more flexibility in organizing email sending and can be used to create specific streams for transactional and broadcast messages. The integration also enables the use of Postmark's Broadcast sending capabilities with Zapier, making it easy to trigger promotional or bulk emails. Users can leverage this integration to automate various tasks such as sending emails when someone completes a form, adds an address to a Google Sheets row, or receives notifications when an email address bounces. With thousands of supported apps in Zapier, users have unlimited ways to build custom automated workflows with Postmark and Zapier.