As part of the reorganisation of the notification menus (T123018), we need to change the representation of one of the badges. While "alerts" still conveys the idea of the most urgent notifications, "messages" (with the talk bubble icon) no longer works since there will be notifications not related to conversations (e.g., a page being linked).
An inbox tray has been proposed as a generic way to rpresent the non-urgent notifications ( other concepts were explored at F4000095):
Example in context:
If there are no issues, the icon should be integrated to the standard icon repo(s).
In the vector file, I based the spacing around the shape in the "Bell" icon, since it will appear next to it in practice, but please let me know if there is any other consideration I'm missing.