How subscribe to a "message thread"?

There's a thread/topic that I want to follow, but don't need to post into that thread (at the moment)...

I can't find any way to subscribe to that thread/topic. Is posting a message there the only way to subscribe?

Thx.

At the top right corner of the thread, you will see a button "Receive Emails" Click that button. You will see a variety of notification options. I always just set it to "Receive Alerts and Emails", so I don't know whether any of the other options work.