Mobility: Everyone has a cell phone these days, and those are increasingly smartphones that are used to deal with email. Thanks to the iPad and its imitators, the tablet market is growing quickly. Not to mention how much SMS messaging is being, especially by people who rarely use email.
Social Networks: Something like a third of the global population is on Facebook, and a huge number are on Twitter. Increasingly people are using those for communication where they would have used email before. (Due to spam filtering they're also more reliable than email.) And much of this is happening with mobile devices that work less well with email.
I can very much see why Sendmail Inc would want to be involved in these things. As a company, their survival depends on it.