"More than likely it was a default option; the software
is there, so why not use it? Why? Because there might be something
out there that suits your needs far better. Other email clients can
be highly customised to suit particular industries and may include
options not available in Outlook.
"How much you can expect from an email client depends on your
company size and procedures for communication. For example, many
organisations must have shared calendars, while other companies can
be quite efficient with individual calendars."