I've written a few times before about the spread of Software as a Service (SaaS) in the messaging and collaboration market. For example, there are several well-known message hygiene SaaS offerings, including Microsoft Exchange Hosted Filtering, Google's Postini, and MessageLabs; there are also entire applications or application suites, such as Salesforce.com and Microsoft's hosted CRM, Exchange Server, and SharePoint offerings. If you're considering using a hosted service for messaging and collaboration, what should you be looking for? More importantly, what should you be looking out for?

Let's start with the elephant in the room: service availability and quality. Any time you use a hosted service, you're putting yourself at its mercy. Google recently sent a message to subscribers about its series of August outages. In essence, the message was the sort of almost-apology common from large corporations who have let their customers down in some way; it expressed regret for the outage and offered some vague platitudes about how Google is working to keep outages from happening in the future. (See my blog entry, "Google: we're almost sorry about our outage,"  for a more detailed dissection of Google's message.)

One of the advantages of SaaS is that it's supposed to free you from worrying about maintaining high availability for critical services; any service that can't do that isn't worthy of consideration for business use. Look carefully at the history of outages—and the service provider's track record of communication and transparency—before you plunk down any money.

Next, what about migration? If you're setting up a new organization from scratch, you might not think of this as a big deal—but it could become a big deal later when you want to move your accumulated mail and calendar data to a different platform. Exchange offers IMAP-based migration through the Microsoft Transporter Suite so you can easily move data in and out, but the migration story for SaaS messaging isn't nearly as clear. Premise-hosted solutions such as Exchange tend to be quite sticky because migrating away from them can be difficult and expensive; SaaS vendors would like to encourage this same degree of stickiness, but it's hard to do. Google in particular is a great example: They don't provide any native migration tools to get data into or out of Google Apps Premier Edition, which should certainly give you pause.

Finally, there's the question of functionality. There's no serious argument: Microsoft Office Outlook 2007 is the most full-featured messaging and calendaring client available, which is why vendors such as Google, PostPath, and Scalix make so much noise about their back-end systems' ability to work seamlessly with Outlook. However, Microsoft has a steady tradition of providing "better together" functionality that requires both Exchange and Outlook to deliver full capabilities. Google appears to be making more effort in this direction with Chrome, which is more an application runtime (think "offline Gmail") than a browser. However, in most cases SaaS systems lack functionality found in self-hosted systems, so you should be sure to check into whether SaaS solutions you investigate have all the features you're currently using.