I didn't see this mentioned before so here it is.
I would like to see the spam filtering options ability to be enabled or disable by user and domain. I have some domains and some users in these domains that would like to get all mail regardless of whether or not it's spam.
It would be great to say to a user or a domain admin that I can turn it on or off for them. Also this would be more incentive for people using the free acounts to want more options. Just add an option for each user/domain that would enable/disable filtering, greylisting and other spam options.
If there is already a way to do this I missed it.