There are differences in the subscription system between paid accounts and free accounts.
Free accounts cannot subscribe on all boards(General for example),
have fewer results shown on their subscriptions list, no default to
Disable Automatic subscriptions, Subscribe without Email Notifications,
or Subscribe with Email Notifications, no ability to Change the
Subscription Option at the time of posting (Do Not Add to Subscribe
List, Without Email Notification, Subscribe With Email Notification).
If the subscribe button isn't present then you are in a community, i.e.
General, that you do not have access to the subscription system for.
As a free account you have to subscribe to threads manually and set the email option to on.
On your subscriptions page threads that you want to receive email updates from should show this symbol
not this one
Just click to switch.
Additionally threads you have created are available under MyTopics
subscriptions=threads you have subscribed to, via posting or marking as subscribed.
My Topics=threads you have started
My Board
=forums you have marked as such will show up as a custom community for you under MyBoard
Active Topics=Topics most recently  posted in.