mass mailing delay between emails

I tried to send VB mass mailing,
I set Email to send at once to 50,
I have over 6000 users but on the user number 2111 server is freeze (Stop responding).
customer service answer that: "We have a limit of sending mails on the server. The maximum number of emails that a domain can send per hour is 1000.
If you need to send more emails, make sure that you use some kind of batch process to put a delay between emails."
Is there any opportunity to make delay between emails?
thanks
Alexei

I think I just saw a hack on vbulletin.org to send emails with a cron job. If that doesn't help, I also think I saw there another modification to send all the email messages in batch (usefull for busy forums with a lot of subscriptions). I don't have the links right now, but I'm sure you can find them with a quick search.