Although the new-and-interesting Office 365 Groups have taken some of the shine and luster off site mailboxes in terms of the collaboration options that are now available in Office 365, some companies have site mailboxes deployed because they like the way that site mailboxes exploit Exchange mailboxes and SharePoint document libraries (for the 2013 on-premises versions or their cloud equivalents). I’ve used site mailboxes productively for project-level collaboration in the past. The big advantages offered by site mailboxes over Groups are that:

1. Site mailboxes can be used in on-premises deployments, including hybrid deployments if both SharePoint libraries and Exchange mailboxes are on the same platform (cloud or on-premises). Groups are not currently available for on-premises deployments.
2. Site mailboxes are accessed through Outlook 2013 rather than Outlook Web App (OWA), which is the only client supported by Groups. However, you must deploy the Professional Plus version of Outlook 2013 if you want to use site mailboxes.

Outlook 2013 can open a maximum of ten site mailboxes. This might seem an arbitrary number because it is possible that someone might contribute to more than ten projects at one time, but some good sense lies behind the limitation. First, there’s the question of usability and screen real estate. Every site mailbox requires a certain amount of space to be displayed in Outlook’s list of available resources alongside a user’s primary mailbox, perhaps an archive mailbox, some favorites, and maybe even a PST or two. In short, the resource list can be a pretty cluttered space even without site mailboxes.

And then there’s the question of performance. Every site mailbox that Outlook has to open requires memory to map the folders and items held in the mailbox. Allowing Outlook to open more than ten site mailboxes might exhaust some system resource and cause slow performance. Ten seems like a reasonable compromise between functionality and preventing site mailboxes becoming a drain on system performance.

So what happens when you fall into the happy category of being so busy with so many projects that you are a member of more than ten SharePoint sites that include site mailboxes? The answer lies in the “Manage All Site Mailboxes” option that is revealed when you right click on the account name in Outlook’s navigation pane. This option forces Outlook to open the “my site mailboxes” page that is actually under the control of Exchange as evident with its URL (usually something like https://contoso.com/ecp/TeamMailbox/TeamMailbox.slab). You can use this page to decide which of your site mailboxes should be displayed in Outlook. It’s as simple as that. The changes that you make will be effective as soon as Autodiscover publishes details of the new set to Outlook either the next time you start the client or as a result of its regular 15-minute refresh.

If you’re still struggling with the finer details of an Exchange 2013 deployment and can’t yet face into deploying SharePoint 2013 so that site mailboxes can be used, why not consider signing up for an Office 365 test domain? Apart from letting Microsoft do all the heavy lifting to install and configure Exchange and SharePoint, this approach is a great way to establish a sandbox environment where you can test new features, including site mailboxes, at your leisure.

Happy collaboration!

Follow Tony @12Knocksinna