Rolling out a new email system

You'll save yourself a great deal of time and misery across the board to keep the operating systems, hardware, and users in mind as you draw up your implementation plans. People do the darnedest things and the odds are there that the two things most likely to bite you are going to be the users when you do deploy the new service, and the hardware. So be sure to budget extra time to deal with user issues and issues users will create - and extra money to replace that one or two pieces of hardware that will not cooperate no matter what you do.
If you can, do some virtual research and see how the various hardwares and operating systems perform with the new email service. You can't predict people but you can get a good idea fast what will happen with the rest going that route.

If you're setting up an all new system you need to find out how the users are currently communicating in house. Besides the intercom and phone system. Then since it's a hospital pay attention to what they're going to use the email for - whether it's strictly in house or to communicate with the public - but security needs to be in mind every step of the way. IMO.

I don't know what the foundation of the system is - hardware (is it old new blah blah) - but first pay attention to the network hardware. Those routers and hubs may not be able to do the job - 512k just won't cut it anymore in most cases. You may need to add more or replace what exists. Those will also give you a good idea of the shape of the existing systems - if what you're working with is fairly up to date then most likely you won't have to deal with too many legacy issues with the hardware.

The operating systems on the workstations and what they're using for network security already would be next. Look into and be ready to deal with known issues between the operating systems and the email server software. Then the email service and network security - be prepared to reconfigure or even reinstall or replace that en masse.

And the users. People love new toys but there's always someone who'll try to break yours. The odds are there so I figured I'd bring it up. Make sure to take the time to set up procedures that are simple and effective. Keep a solid list of names and passwords - they are most likely to be lost or confused or forgotten the first two weeks of deployment.

Custom software. Keep that in mind too as you make decisions. Even if it's not your stuff to oversee - make sure to know that stuff in and out. Odds are it's mission critical and they must have it - so be very certain that your new service doesn't hinder it's use, effectiveness, or create issues.

For better or worse, regardless of the alternatives you offer, people like to send files as e-mail attachments. Users don't know the difference between attaching a 500 kilobyte cartoon and a 25 megabyte 12-megapixel chest x-ray, and they don't think anything of sending at attachment to twenty other people. Be aware of the amount of storage space you'll need.

I can't speak for your side of the Atlantic, but over here the retention of medical information is covered under federal law. Be sure you have an adequate backup system, including permanent off-site retention of monthly data (or more frequently). You'll need a way to retrieve that information when a malpractice lawsuit pops up.

A widely deployed LAN/WAN exists in the hospital but its mainly used to support the Clinical systems but there's a cable drop into all offices.

Of the 350 machines targeted to get mail only 10% are what could be classed a "Modern Machines"