Exchange Online to Drop Support for Older ActiveSync Client Versions

Microsoft is taking a firm step to strengthen security and reliability for Exchange Online customers. The company plans to block devices using Exchange ActiveSync (EAS) protocol versions earlier than 16.1 from connecting to Exchange Online in 2026.

Exchange Online ActiveSync (EAS) is a protocol that enables mobile devices to synchronize email, calendar, contacts, and tasks with Exchange Online in Microsoft 365. It uses HTTP and XML to provide real-time access to mailbox data, which allows users to stay connected across smartphones and tablets. EAS ensures secure communication and efficient data syncing that makes it an important technology for native mail apps on iOS and Android.

Which devices and apps will be affected?

Starting on March 1, 2026, Microsoft will require email clients to use Exchange ActiveSync (EAS) v16.1 to connect to Exchange Online. This update will primarily affect customers using mobile devices with native email apps to access Exchange Online mailboxes through EAS protocol. However, it doesn’t affect on-premises Exchange Server or mobile apps that don’t rely on EAS, such as the Outlook mobile app.

“This decision comes after extensive collaboration with multiple licensed device and application vendors to ensure a smooth transition for as many users as possible. If users and organizations keep their devices and applications updated to the latest supported versions, there should be minimal service disruption. We encourage everyone to verify their devices and applications are up to date before the change takes effect,” the Exchange team explained.

How can IT admins identify outdated EAS clients?

Microsoft is encouraging organizations to verify that all mobile devices and apps are updated to EAS version 16.1 or higher before this change takes effect on March 1, 2026. To identify devices still using outdated EAS versions, admins can run this PowerShell command:

Get-MobileDevice | Where-Object {($_.ClientType -eq 'EAS' -or $_.ClientType -match 'ActiveSync') -and $_.ClientVersion -and ([version]$_.ClientVersion -lt [version]'16.1')} | Sort-Object UserDisplayName | Select-Object UserDisplayName, UserPrincipalName, DeviceId, DeviceModel

Microsoft is making this change to strengthen security and improve reliability by eliminating older versions of the Exchange ActiveSync protocol that lack modern protections. Outdated protocols can introduce vulnerabilities and compatibility issues, and moving to EAS 16.1 ensures better encryption, stability, and compliance with current standards. This upcoming update aims to reduce risks, maintain a secure Exchange Online environment, and encourage organizations to proactively update devices to avoid service disruptions.