Customizable Outlook Mobile Synchronization Between 1 and 90 Days

A change so good that Microsoft announced it twice in MC696167 (7 December 2023, last updated 24 May 2024) and MC798682 (last updated 14 June 2024) tells us that Outlook Mobile users can customize the synchronization window for their device. Both are associated with Microsoft 365 roadmap item189809. According to MC798682, the rollout started in early June and was expected to finish by late June 2024. I didn’t see the update until July 2.

The synchronization window defines the period for downloading email and attachments to a device and enables offline access to mailbox contents. MC798682 says that the period extends between one and 30 days, but as you can see in Figure 1, the iOS client offers the ability to synchronize data for up to 90 days. Microsoft says that they will expand the size of the synchronization window from 90 days after they confirm that everything works well in production.

The now-renamed Outlook classic client has had a customizable synchronization period since the introduction of “drizzle mode synchronization” in Outlook 2013, but this is the first time that the iOS and Android clients get similar control.

Synchronization Basics

Synchronization happens between Outlook mobile and the cached copies of user mailboxes stored in Azure. Being able to set a minimum one-day window might seem strange, but it addresses the need some organizations have to restrict the amount of corporate data stored on a device. If messages outside the window are needed, Outlook mobile can fetch them from the server if a network link exists. It just takes a little longer than if the messages are cached locally.

Previously, Outlook mobile synchronized 500 items per folder by default with the ability to download up to 1,000 items per folder if necessary. Outlook periodically trims the data cached on the device to keep the items under the configured limit. With the introduction of the new synchronization window., Microsoft is limiting download to a maximum of 2,000 messages. Restricting the number of messages downloaded to the local cache makes sure that the Outlook mobile client can function without problems, especially on low-end devices. Microsoft says that they’ll increase the maximum for synchronized items and the size of the synchronization window in future versions of Outlook mobile.

Configuring the Synchronization Window

To configure the synchronization window, select the Settings option in the client. In the General section, select accounts and then the account for which you want to configure the synchronization window. Go to the Data storage setting and configure Sync settings with the number of days for the synchronization window (Figure 1).

You can also toggle the Include attachments option on or off to control if Outlook mobile should automatically download message attachments received during the synchronization window (Figure 2).

Through Intune controls, administrators can set a default synchronization window for devices and stop users changing that window. The keys for the two settings are:

• com.microsoft.outlook.Settings.DaysToSync.
• com.microsoft.outlook.Settings.DaysToSync.UserChangeAllowed.

The maximum value settable through Intune for the synchronization window is 90 days, which is the same as seen in the client.

Outlook Monarch Gets Synchronization Too

The first support for offline access in the new Outlook for Windows (aka Monarch) was also due to begin its rollout in late June 2024 (MC798674, Microsoft 365 roadmap item 178030) covering mail, calendar, and contacts. Only a limited set of actions are covered, including the important ability to read and send email. So far, I haven’t seen the update or heard of others receiving it, but worldwide deployment isn’t scheduled to finish before late July 2024.

This is an important step forward for the Monarch client, which is already generally available to consumer users (and not without some controversy due to the way that Monarch synchronizes mailbox data from Azure). Microsoft knows that Monarch isn’t ready for prime-time exposure to corporate users yet because features like offline working haven’t been available until now. There’s still a bunch of work to do here before Microsoft can retire Outlook classic in 2029.

Everyone Wins with a Customizable Outlook Mobile Synchronization Window

Synchronization is not rocket science at this point. Adding a customizable synchronization window to Outlook mobile makes sense. It allows Microsoft to address some customer concerns about having too much corporate data on a phone while those who would like to carry around their entire mailbox might be able to do so in future. Everyone wins.

So much change, all the time. It’s a challenge to stay abreast of all the updates Microsoft makes across the Microsoft 365 ecosystem. Subscribe to the Office 365 for IT Pros eBook to receive monthly insights into what happens, why it happens, and what new features and capabilities mean for your tenant.