Gmail's recent inbox update has placed all marketing emails into a new "Promotions" inbox, causing frustration in the email marketing community. To get around this, Postmark is testing various methods to ensure transactional emails from customers reach the Primary inbox. After conducting tests, they found that changing the return-path header domain to match the From header domain worked consistently, but also stopped bounce processing for their customers. However, excluding the "List-Unsubscribe" header allowed emails to go directly to the Updates folder, which is not enabled by default and places them in the Primary inbox. Postmark feels comfortable removing the list-unsubscribe header since they are a transactional-only sender with good Inbox rates, but will monitor complaints and abuse closely if a traditional Feedback Loop system is added.