“It’s been a while since I’ve had to put together a messaging
solution for a client. For smaller businesses, it’s usually easier
to point them to a solution like Gmail Apps for Your Domain, while
midsize businesses can be ramped up to Exchange or Zimbra, should
they need it.“There’s another open source messaging solution, though, that
scales quite well into the SMB space, and it gives you the
flexibility to install locally or use it as a software as a service
utility: Open-Xchange.“Actually, since its beginnings as an Exchange alternative for
SMBs, Open-Xchange has stretched a bit beyond just “messaging
solution,” although it still manages to do that pretty well. The
flagship product, Open-Xchange Server, is regarded as a full
collaborative platform, particularly with the addition of the
Infostore document sharing module.”