[imp] Spam problems

[Ricki Levitan]

 Hi,
Sorry if these sound like rookie questions, but hey, I'm a rookie!
I have a client who hasn't wanted any spam filtering applied because she's self-employed, has clients all over the world who send files, and doesn't want any legit email to be missed.  It's worked well for a few years, but spammers have found her - with a vengeance!
Couple of questions:
She tried logging into her Horde webmail and right-clicking / blacklisting hundreds of emails. That not only didn't work, but it seems to have increased the number of spam emails.  And now she's getting duplicate spam messages about half the time (and I'm talking 100's per day).  Beyond marking them for blacklisting, is there another step that needs to be taken to actually have these addresses blacklisted?  I know that's not a catch-all solution as they change all the time, but it should have helped at least a little.  (I've had a Hotmail account for more years than I care to let on, and the spammers finally found me about a year ago / built up to about 500 per week. They landed in the junk folder, appropriately most of the time, and when I started blocking the spam messages it worked like a charm and now I'm only getting about 30 a week.  I was hoping that by her blacklisting them the same thing would happen for her, but not so much.)
What else can be done to help stop this onslaught?  Is the only answer using BoxTrapper or SpamAssassin?  What are your preferences and do you have any helpful tips to be on the lookout for, for someone who will be setting up one of these services for the first time?
I've been thinking about website hosts anyway, and of course her mail would be moved to the new host.  Would that be of any benefit (until they find her again)?
Any help you could provide would be greatly appreciated!!