100 is relatively small.
Last email I set up was for 3000 with a couple of spark5's with a couple of NIC's each # linked to a solaris file server with samba running the file system to link to PC's on the back of NIS+
Worked a treat and the load factors never got above 0.6 Only down time was planned.
There was mucho moaning from across the atlantic about joining the exchange enterprise but that would have cost an absolute fortune in hardware and licenses and 3 admins. Job done for 2 recycled work stations and about 5 hours a month admin patching after setting up all the cron jobs.
Was still running 7 years ago and had been up for 5 years. How much for 3 exchange servers for 3000 users and licenses for 5 years?
Even though I am an ATPL I still have a black belt in vi and still have all my old scripts.
Will let you know how its goes I may through throw caution to the wind and get 5 raspberry's and 5 rechargeable battery packs which will bring the hardware price up to 250 euros.