Re: How much?
Apols for my regular late response :)
I doubt that Microsoft are just going to shut down Office 365. It's one of their most profitable businesses and what they see as the future of their company.
Shut it down? Maybe not. Change terms, remove your data, suddenly cut your allowance etc? They've done that. Decide features are not going to be supported any more despite a large % of their userbase begging them to retain it? They've done that a few times.
What about the legal implications? Do you work with other people's information? What of the privacy laws where you and your customers are based - can you survive having client data sent to MS? I'd hate to discover my Dr had moved to W10 (they haven't as yet), and will be making things a bit more difficult for them if they do, until I am satisfied that their IT arrangements meet the rights I have RE data protection/privacy. Same for any one else.
I have offline copies of our emails. And I control our domains. So if it suddenly disappears I'll have to scramble to set up some other email service and deal with it the best I can.
I ran ours on an old laptop, admittedly that only supported a few staff and also some friends were given access for the hell of it/testing purposes. Perhaps 10 people/accounts in total. Didn't take much to set up (perhaps a weekend) and maintenance was trivial.
I also did my own jobs as well as supporting our customers. I did web design work, some on my server some on other arrangements, and a fair bit of other stuff, supporting Windows Mac and Linux. Oh and Android (we didn't do IOS stuff but more from a lack of experience than anything else).
Admittedly I did work many more hours than the shop was open, but it was mine and I was intent on making it work. (small tip for business success, don't hire a lying cheating thieving bitch as a business manager!)
At the moment that's me, but I'm not competent to manage an Exchange server, and have no intention of learning. I support our PCs and deal with IT in the breaks between actual paying work.
--> There's enough effort in supporting PC's days so I don't blame you on not doing Exchange! :) I honestly am happier being (mostly) out of it.
For a large company, there are much better alternatives. For a company our size cloud is far more reliable and cost effective than what we can do ourselves.
As you've probably seen, I'm a cautious cloud advocate. I've seen come firms die or majorly change (Mega could go the same way as Megaupload, copy.com was decent but suddenly cut storage services, MS has changed/cut storage services and other things, AWS commonly gets hacked (usually due to user error but not always it seems). I do from time to time use other services where they can provide better than I can but I strongly advocate if you use another's computer make sure you keep your own copies of data (properly backed up) and if you cannot back up the software then have a way of replicating it (even if just saving to standard formats rather than proprietary).
Couple of years back we had the Kaikoura quake, which was interesting on both sides of the cloud debate. Some buildings were damaged so much that people were not allowed to even remove parked cars from the streets outside let alone go in to retrieve computers. Anyone with all their data on-prem and no where else was screwed whereas places with all their data in "the cloud" would've been OK.
OTOH, areas were without power for a while (12 hours for my suburb so not bad, but others were out for a while longer) and coms were down in places as well. Those with all their data available and mobile enough to move would be OK, those with power but no internet could not use cloud anything.
We've had large-scale internet losses (whether a telco's systems go TITSUP or 'natural disasters" knock out coms lines) as well. Oh, and un-natural ones like the idiots at Chorus who list "single digit IQ" as one of their prime qualifications it seems (Chorus manages most of our telecoms infrastructure).
I guess I advocate backups by whatever means gets you running quickly. Me - had our shop server and had another machine in a mate's closet, now have the two split up across geographically different areas. When we had a long-term outage I was able to change DNS entries to the backup system once I drove far enough to get a connection.
But yes, I wouldn't want to manage exchange either :) I did owncloud for data and calender stuff (pretty much outta the box setup) and IIRC "Flurdy" was the guy who wrote the email tut I followed. Apache+PHP for the web stuff. (IIRC - been a while since I actually had to pay any attention to it!)