[exim] Front End

Our senior management keep on about "Modern Email Solutions", and
complain that we do not offer any form of collaborative working, such as
personal and group diaries and calenders. Now we love exim as an MTA but
there is a lot of pressure to switch to something with all the above.
Does anybody else have this pressure, or does anybody have a good group
diary/calender solution that they use in conjunction with exim?

Ron