repeated email reminders

Hi,
the system sends repeated emails to a user who has registered but not fully completed the 4-step process, it reads:

You have registered on our website but you have not completed the procedure yet.
It will take just two minutes to finish the registration. You will not be disappointed!

If i close the user 4-step window then it stops.
Is there a way to stop this annoying behaviour?
I think 1 message per user login session is enough.

thanks, nigel