OOT: Spamhaus professional service

[Budi Febrianto]

Hi,
I just move out to another company, that the size is bigger than the 
last one.
I want to use spamhaus in mta level, but know I worried about the size.

based on
http://www.spamhaus.org/organization/dnsblusage.html

I wonder, can I still use the free service, or I had to use the 
professional service?
Number of user aprox 500 users, and it may double next year.
I still don't kwnw how many emails we are receives everyday because 
rigth now we are using mdaemon as mail server. I plan to move it to 
mailscanner with zen.spamhaus.org
Anybody still using spamhaus with the same user or maybe even larger 
users? Any problem?

Thanks