do I understand it correctly: you (1) have 30 pre-defined classes of emails, (2) you predict a class, (3) put email in a specific UI? I think dynamic clusters would be more helpful! every inbox is different. what if you would cluster my inbox and predict a cluster for a new email? you can do that based on the content and interactions.
The groups/topics are indeed dynamic! A slightly different set for each user. I wrote ~30 because those many are the categories + subcategories a user's emails roughly spread across. And it's still simple and intuitive to browse over:)