Place filtering power in the hands of the players!

[Risvertasashi]

creating a feature such as email spam filter would require more effort

It's actually pretty easy with the use of what's known as Regular Expressions. There's third party addons that do exactly this for RMT tells, but sadly we can't really talk much about those here. If SE would actually deliver on their promise of official addon support we could do this pretty easily.

Problem is: g0ld, .co m, de livery, just bypassed your filters.

There are actually programming languages (perl and it's accompanying regular expressions mainly comes to mine) that allow for approximate matches (i.e. if it's just an extra space or changed letter it still matches), recognize that '0' can also be 'o' and other such common substitutions.

These aren't unsolved problems. Of course one has to be careful, lest they accidentally match legitimate messages. But with addon support we could decide for ourselves what filtering methods to use and how aggressive to make them.