Why Amazon Is Getting Into Business E-Mail - Bloomberg Business

Check this Amazon page for more WorkMail details; I suspect IBM would disagree with the "only two major competitors" (Microsoft and Google) assertion

"“You’re coming into a very established place with only two major competitors,” said David Mitchell Smith of market research firm Gartner. “They’re not coming in at the leadership position, that’s for sure.” 
That has never stopped Amazon before. And in a time when hacking and security issues are a growing concern in the business world, a new service with an express emphasis on privacy could make a dent in the e-mail game while bringing more customers into the Amazon fold.
The only surprise here is why it took Amazon so long."

Why Amazon Is Getting Into Business E-Mail - Bloomberg Business