Don't know so much about this feature in other softwares then vBulletin but you can choose no notification, notification, email notification and so on. What do you have as default for all members on your board?
My default settings are that new members will be automatically subscribed to threads with instant e-mail notification.
I noticed that! My emails are arriving! On my forums that are popular it is set to subscribe with no email. On my not popular forum subscribe with email.
Daily Notification this way if someone signs up and starts posting right away they don't get inundated with 'spam'. Don't laugh, I've actually had new members call it spam. As a member if it's a board where I'm going to hang around, I always choose no email notification. If it's somewhere I'm going to post a few times I'll choose weekly unless I'm looking for information than I'll change it to instant for just that one thread.
I set my new members to instant email notification, but I generally turn off notifications entirely when I join other people's forums.
When I join other forums, I set it to "No E-mail Notification" if I am going to stick around. If it's a support forum and I'm only there to get help, I will use Instant E-mail Notification.