it's just not that easy.
Professional spammers are using every possible trick to disguise their mails as non-spam. At the same time many non-spam mails (private messages or business correspondence) can contain single words that also frequently occur in spam mails.
The learning filter now has to decide if a single mail is spam or non spam, based on the words that occur in the mail. It often takes some time (mostly a week) until the learning filter has accumulated enough data to mark a certain type of non-spam-mails correctly. The same applies for spam-mails. In general, you'll discover, that after 2 weeks of using Spamihilator (including the training of the learning filter), Spamihilator will mark approx. 95% of the mails correctly.
You can further enhance the success rate of Spamihilator by the use and adjustment of the other filters. The easiest way in this special case would be to put the sender of the wanted mails in the friends-list, which means that the mails will always be treated and marked as non-spam.
Well, "learning filter", "training", "adjustment", "maintenance of friends-lists" etc., that might sound like much work, but it isn't. I'm using Spamihilator since 2007 and it really has saved me a lot of time. Before I used Spamihilator, the daily cleanup of spam-mails mostly took more than 15 minutes. Since I use Spamihilator, my daily anti-spam-work rarely takes more than 5 minutes and it has become much less of a hassle.
To make it short, just use Spamihilator for a week or two and get accustomed a little with the filters and options and you'll see how it makes your daily anti-spam-work much easier.