Email is <A HREF="http://integrate.factiva.com/search/showarticle.asp?AN=BSTNGB0020040816e08f0004o&vfrom=sch&MODAUTOLOG=S000WJj2sr75DMn5DEmOTIsN9MvNpNyMHmmVqfgMdNoNqFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQQAA&LWS=1">a victim of its own success.</A> That's the conclusion of IBM researchers in Cambridge, who have spent nearly a decade conducting field tests at IBM and other companies about how employees work and use electronic mail. It's clear to them that email has become the Internet's killer application.