Why am I still getting some spam?

Dealing with spam is not an exact science, spam filters have a variety of processes built in to evaluate messages as to whether they are spam or legitimate, and unfortunately there is not hard and fast rule that fits every case. There are lots of messages that fall into a grey area, and sometimes these emails can slip through, because it is a machine evaluating it, not a human. So where you or I would only have to glance at an email and determine with a reasonable degree of accuracy whether it is legitimate email or not, spam filters have to operate on the rules they have in them.

As the spam filters get new rules, so the spammers up the ante and try new techniques, which then have to be caught, analysed and blocked, and this leaves a small window of of opportunity for these new spam emails to slip through.

With all this going on, it is almost impossible to guarantee 100% no spam, as it is a case of best effort, which blocks the vast majority of spam from being delivered.