As an Office 365 MVP, I’m fully convinced the platform Microsoft has built for communication and collaboration in the cloud is solid. Not only that, but I believe a Microsoft SaaS monopoly in the near future is inevitable, considering the fact that on-premises Exchange holds a huge percentage of the email server market.
It’s important, therefore, to understand the various Office 365 plans offered, the limitations of Office 365 compared to its-premises counterparts, and the service-level agreements offered.
Let's start with the plan you choose for Office 365. Microsoft has a useful comparison chart, but they basically fall into two groups: small business (300 seats and fewer) and enterprise (more than 300 seats). Both groups have three subgroups: cloud servers (Exchange, SharePoint, and so on), Office suite (the productivity apps but no server tools), and both the cloud servers and Office suite.
The complete enterprise Office 365 subscription runs about $20 per user per month, and it includes a variety of features you may not need or want. But Microsoft's comparison page doesn't really show those other features. A complete view of the tools is available in TechNet's Office 365 Service Comparison page. That page will tell you whether the $20 E3 plan is overkill and perhaps guide you to the cheaper E1 plan supplemented by old-fashioned perpetual Office licenses instead.
Now let's consider Office 365's limitations. They change from time to time, so you need to keep abreast of the current limitations. For example, file attachments in Exchange Online were initially limited to 25MB, and if you set up a new portal you still see 25MB as the default setting. But if you review Microsoft's Exchange Online limits document, you see that the new message limit is 150MB for Outlook and 112MB for Outlook Web App (OWA) -- if you send a message outside a Microsoft data center. Otherwise, you can send 150MB. (Of course, there is no guarantee the recipient is allowed to receive attachments of that size. In fact, it's more than likely they aren’t.)
Finally, let's examine the service levels you can expect from Microsoft for each plan. You'll find those -- plus capability descriptions for self-support -- in TechNet's Office 365 Service Descriptions section. In these service descriptions are links to the plan comparison data and the limitation data I mentioned, but you also get links to details on individual features, so you can learn exactly what Microsoft promises to provide to your organization.
Now is not the time to merely sleepwalk into Office 365. Take advantage of the information Microsoft provides to make the right choices and have the details you need to manage your Office 365 environment well.