If the goal is to simply mark all 25,000+ emails as read to remove the unread notification badge, follow this procedure on a desktop browser: (not mobile).
Here is a complete write-up on accessing and clearing a massive backlog of emails: 1. The Strategy: Bulk "Mark as Read" (25k+ Emails) 25k mails access.txt
Click the "Mark as read" icon (envelope icon) in the top toolbar. 2. The Strategy: Bulk Deletion (Clearing Storage) If the goal is to simply mark all