Adding Support in Outlook Mobile for Exchange Online Archive Mailboxes

Microsoft has a history of confusing Outlook users when referring to archives. The archive folder is part of the set of default folders created in every mailbox. Years after its introduction, I still can’t work out why Microsoft thought it was a good idea to include an archive folder. After all, if people want an archive folder, they can create it themselves.

When I last wrote about the archive folder to recommend how to stop the backspace key moving items into the folder (probably the way that most items end up there), I noted that Outlook mobile clients could synchronize the archive folder but couldn’t access the online archive.

The online archive is a special form of mailbox that can expand by adding “storage chunks.” Fully expanded, an archive mailbox can hold up to 1.5 TB, which is a lot of email. Many enterprise customers use mailbox retention policies to move items to archive mailboxes after a set period before eventually removing the items after a further period lapses. The ability to move items to archive mailboxes is something that Microsoft 365 retention policies cannot do. Fortunately, the Managed Folder Assistant supports running both types of retention policies to maximize the benefits of both.

Updating Microsoft Synchronization Technology for the new Outlook

The Exchange ActiveSync (EAS) protocol never supported access to archive mailboxes and never will. Don’t expect to use the Apple iOS mail client or other EAS clients to explore the contents of an archive mailbox. Microsoft has no interest in adding support for archive mailboxes to EAS and email client developers don’t see the need to expand their UI to support archive mailboxes.

However, the new Outlook for Windows client needed to support archive mailboxes to meet the expectations of enterprise customers and have any chance of dislodging Outlook classic. Microsoft therefore updated the synchronization technology to support access to archive mailboxes. Because Outlook Mobile and the new Outlook for Windows use the same synchronization technology, Outlook Mobile can open and interact with archive mailboxes, as described in message center notification MC896712 (24 September 2024).

The update is rolling out to mobile devices for both iOS and Android and should be complete by late October 2024. Before a mobile device can access the online archive, the primary mailbox must be archive-enabled. You can do this in the Exchange admin center or with PowerShell. Here’s a handy script to archive-enable mailboxes after they reach a certain threshold.

Accessing Items in an Archive Mailbox with Outlook Mobile

I’ve used an archive mailbox for as long as Exchange supported the feature, so I have a mass of information in my archive. Accessing the information is easy because Outlook mobile lists the mailbox in its resource list. Clicking on the mailbox reveals its folders (Figure 1).

Outlook mobile uses a configurable synchronization window to choose how many days of email to download to the device. In most cases, items end up in an archive mailbox through retention policies, which means that they must reach a certain age before the Managed Folder Assistant moves them from the primary mailbox to the archive.

Take the example of the folder shown in Figure 2. The folder relates to an event I was involved with in 2016 and stores items relating to the organization of the event, presentations, and so on. However, when Outlook mobile opens the folder, nothing is there. This is because all the folder items date from 2016 and are well past the 90-day window I use to download items to Outlook mobile.

The solution is to swipe down in the folder. Outlook mobile then prompts with a link to “load more conversations.” Click the link and Outlook downloads approximately 40 items. If you need to see more, go to the bottom of the list and choose to load more conversations.

Probably Not a Feature People Will Use Daily

Given the age of items stored in archive mailboxes and the primary use of mobile clients as email triage devices, access to archive mailboxes might be of little use to many. But being able to open and access items in archive mailboxes can be extraordinarily useful in certain circumstances, and being able to now do this in Outlook mobile is a good thing. At least, I think it is.

Insight like this doesn’t come easily. You’ve got to know the technology and understand how to look behind the scenes. Benefit from the knowledge and experience of the Office 365 for IT Pros team by subscribing to the best eBook covering Office 365 and the wider Microsoft 365 ecosystem.