I was in the middle of the great email battle between Microsoft and IBM [Disclosure: Microsoft and IBM are clients of the author] in the 1990s and there really wasn’t much competition. Microsoft had Exchange, which had its greatest power in its focus on users. IBM bought Lotus to get Notes, which had stronger administration tools and a far better focus on collaboration, but sucked at email. In the end, Microsoft dominated, massively, and Exchange is the recognized standard for business email.
However, IBM just brought out Verse, its new advanced email offering, and it comes to market with many of the same advantages over Exchange that Exchange had over Notes. But, this is email, and experienced CIOs know that changing email is potentially a career-ending process. In order to succeed with a user-focused product you have to get the users excited about it, which may be a skill IBM no longer has.