I use postini, as a spam filter.
it's great.  the university mandates it.
there are a few problems with it, but in general it has cut down the number of emails i get significantly.  great.

the problem comes in the false negatives.  i have to actually go through the list of 100-150 emails per day to fish out approximately 1% of emails that should be delivered.  still, i think it's a good software.

the BIG problem comes from when we want to approve senders of the 1% legitimate emails.  there is a LIMIT ON THE NUMBER OF CHARACTERS on the "approved senders" list.  yes, a limit.  in this day and age.  a software owned by google.  a limit.

the HUGE PROBLEM comes from the size of the approved list: 4KB.

4KB?  really.  four kilobytes.  i can't even imagine that 4KB is something that is measurable in the day and age of Big Data, Terabyte drives for under $100, and 10GB free email accounts.

four  kilo  bytes.

shame on you, postini...