shtml attachment files ?

[mailscanner at barendse.to]

Hi list

I tried blocking \.htm$ and \.html$ in my filename.rules.conf before but 
found that this effectively blocked nearly each and every email that was 
coming in so I have to allow that for as long as MailScanner cannot 
differentiate between an attached .html file or html text in the mail 
itself

Just received another fake/phishing email with an .shtml attachment which 
includes server side includes google taught me.

Would it be OK to block that or will I also lose mail? If, then maybe 
it's a good addition to the standard MS filename rules?

Thanks!