E mail and user registration problems in joomla 1.5

Closed - This job posting has been filled and work has been completed.
Hourly Job
As Needed
Less than 1 week
Intermediate Level
I am looking for a mix of experience and value

Details

I would like to know if you can help me WHITIN THIS MORNING about a problem with email spam. I have joomla 1.5 and for the moment I don't want to upgrade.
Every day I have many user registered to my site, so I deleted all and I have every 2 or 3 days 500 emails send.
So I will need help quickly because I cannot also send e-mail to my customers.