Sending email to many adresses?

I have about 500 customers that I keep informed. I like to send them weekly emails that show my list of stock items. My email provider as most restrict the number of addresses that an email is sent to, I guess because of viruses… At any rate, it is a real pain to list my customers in groups of 50 or less.

Is there a way to get around this?
Outlook Express/ Windows 98SE
Cox Internet email