How might we let people catchup on their unread messages/content on mobile?

**Research insight**

- People are picking up their phones to stay on top of messages, to catch up. The key to that is a way to easily see what's new since your last session in the rooms/DMs you care about.

Some choice user quotes:

**From a professional use case**
> In the morning I just check my phone to see what I've missed and need to action straight away.

> I like to check my new messages when I make my coffee or I'm away from my desk so I can see how quickly I need to get back to my desk

The issue names no files, tests, or implementation entry point. Start by reviewing the research insight and user quotes, then establish a concrete mobile catch-up scope and acceptance criteria; done would require an agreed design or implementation plan for seeing new messages since the last session.

Written by the indexing model from the issue text.