That's correct. If you are a member of a group, you will see a Follow this topic button in the topic header. When selecting it you will start receiving an email notification for each new reply in the topic, much in the way that topic authors do.

Should you wish to discontinue the emails at a later point just use the same button - that BTW will be labeled Mute if your subscription is active.

There is also another option to follow a group as a whole. Once again, if you are a member of a group you will be able to access the group's Email Options tab - see below. This will allow you choose among many levels of group activity tracking, from zero (no email) up to receiving an immediate email for each new entry across the group.

Groups are powerful stuff...