To help trying to avoid inadvertently collapsing a *legitimate* single character, you could maybe use the idea that the "funny" separator is the same between things that should be collapsed. (until the spammers catch on to that)
It will be a not fun day when they do random grouping of chars in their headers, i.e.:

viagra = V *IA *GR  **A

But, ignoring that situation, get the separator, " *", for instance, and remove all occurences. just a thought