Howdy.

> Will the list still work ok if I seperate keyword catagories with a space?

Yes, you can separate entries with any number of hard returns.

>How large can the Blacklist file be before Spamfilter has problems reading or processing email?  How many keyword entries is too many?

That's a difficult question to answer - but it is still a very important one.  Obviously, the answer can vary from customer to customer.  The factors that come to my mind are...

• the processing speed of your mail server
• the rate of incoming messages
  (...those which require scanning - if they're block by a filter before keyword-scanning, then the mail server saves itself some work)
• The length of the text (scanned portion) of the message.
  Obviously, a message that simply says "Why won't you call me?" is probably going to be a lot faster to scan than a message with the subject "201 reasons why you shouldn't break up with me".
• And of course, as you mentioned - how big your keyword file is.  Not only that, but of your keywords, how many of them are RegEx (which require slightly more processing-time)

And speaking of RegEx keywords...  Roberto recently mentioned that it's possible that you may see a performance benefit by putting any RegEx keywords at the bottom of your keyword list.  The idea is that each message is scanned for the presence of each of your keywords, one by one.  If a keyword is at the top of your keyword file, messages containing that keyword will be tagged without having to be scanned for the remaining keywords; so it seems a good strategy to put the "slowest" keywords at the bottom, just in the case that the faster ones will make a catch.

The simplest way to answer your question would be with a load test.  Try sending 3, 5, or 10 messages to your domain at the same time.  Make messages with a lot of text - put that keyword scanner to work!  As you add more and more keywords, see if the performance gets noticeably slower.  If it does so in a worrisome way, it's probably clean-up time for some obsolete keywords.

Stephen