I use dreamhost for my webserver/ email host.

I have about 25 users on one domain. and 1 of these users is absolutely inundated with spam every day.

I have tried using dreamhosts poor blacklist feature, which was semi working (still letting a lot through) but I reached the 1000 email blacklist maximum very quickly.

I have the ability to switch to google apps but that would be very expensive for 25 users.

What options do I have aside from changing hosts with better spam filtering?

I don't think its possible to only switch 1 user to google apps, it has to be the whole domain.

There are other benefits to switching but I don't think they outweigh the cost for this company.