What to Do Before the OWA Light Retirement Deadline in Exchange Server

Microsoft is retiring OWA Light in Exchange Server, with an expected deadline in August 2026. If your organization has users still on the lightweight client, they will lose web mail access when that date arrives. Here is what you need to do, in the order you need to do it.

Why Microsoft Is Retiring OWA Light

OWA Light launched as a stripped-down web mail interface for older browsers and low-bandwidth environments. Microsoft has been moving toward a single full-OWA experience for years. The lightweight client is now a maintenance burden that holds back security improvements and modern authentication features.

The retirement applies to Exchange Server 2016 and Exchange Server 2019. It does not affect Exchange Online.

The Timeline: What We Know

Microsoft announced the retirement via their Tech Community blog. The expected window is August 2026, tied to a Cumulative Update release. The exact version number and precise date can shift, so monitor the Tech Community announcement for updates.

The practical implication: you should treat August 2026 as your hard deadline and plan to have all migrations complete at least a month earlier.

How to Identify OWA Light Users Today

You cannot rely on users to self-report. Most do not know they are on the lightweight client. Here are three ways to find them.

Exchange Admin Center log search

In the Exchange Admin Center, navigate to mail flow > message trace and run a search covering the past 30 days. Export the results and filter by ClientInfo field. OWA Light sessions will show a client value like "Client=OWAred|Version=Black<<<" or similar legacy identifiers depending on your Exchange version. The exact string varies by CU, so look for anything that is not the standard full-OWA user agent string.

Protocol log query via Exchange Management Shell

A more reliable method is to query the protocol logs directly:

Get-MessageTrackingLog -Server "EXCH01" -Start (Get-Date).AddDays(-30) -End (Get-Date) | Where-Object {$_.Source -eq "STOREDRIVER" -and $_.ClientInfo -like "OWA"} | Select-Object Timestamp, Sender, Recipient, ClientInfo | Sort-Object Timestamp -Descending

Review the ClientInfo field in the output. Full OWA and OWA Light produce different entries. Build a list of affected users from this output before planning your migration.

IIS log analysis

OWA Light requests hit a different IIS application path than full OWA requests. On your Exchange servers, check IIS logs for requests to the /owa/auth/legacymail/ directory or similar lightweight-specific endpoints. This gives you an IP-based list of affected machines.

User behavior heuristics

OWA Light users often share these characteristics: they use Internet Explorer or an old version of Edge, they work on older hardware, or they are in remote sites with limited bandwidth. Cross-reference your help desk ticket history for any complaints about OWA slowness or rendering issues.

How to Migrate Users to Full OWA

Once you have identified the affected users, the migration path is straightforward for most of them.

Browser requirements for full OWA

Full OWA requires a supported browser. As of 2026, that means:

• Microsoft Edge (current version)


• Google Chrome (current version)


• Mozilla Firefox (current version)


• Apple Safari (macOS/iOS, current version)

Internet Explorer is not supported for full OWA. If your users are on Internet Explorer, they need to switch browsers first.

Device requirements

Full OWA is not heavy. Any device that runs a current browser can use it. The constraint is usually organizational policy (locked-down browsers, IT-managed installs) rather than hardware capability.

For mobile users: the Outlook mobile app is not affected by this retirement. It is a separate product from OWA. Users who access mail via the Outlook app do not need to take action.

Communicating the change to users

Send a brief message explaining that OWA Light is being discontinued and they need to switch browsers or switch to the full OWA URL before the deadline. Provide the full OWA URL and a short list of supported browsers. Offer help desk support for anyone who hits issues.

If You Cannot Migrate a User

Some users may be on devices that genuinely cannot run a current browser due to organizational constraints, regulatory requirements, or hardware limitations.

For those users, the options are:

• Outlook desktop client as an alternative to web mail


• Microsoft 365 migration if the organization is planning a move


• A planned communication to those users that their web mail access will change, giving them time to adapt

There is no way to extend OWA Light beyond the retirement date. Microsoft is not offering an opt-out or extension mechanism.

Recommended Timeline

Do not wait.

• July 2026: Identify all OWA Light users and assess their devices
• August 2026 (early): Complete browser upgrades and user communication
• August 2026 (mid): Validate that all previously affected users are accessing full OWA
• After the CU lands: Confirm the retirement has taken effect and no users are unexpectedly dropped

Related Problems to Check While You Are in Exchange Admin Center

Infrastructure changes like this are a good opportunity to audit related email settings. While you are in the Exchange Admin Center anyway, check these:

• Verify that SPF, DKIM, and DMARC are correctly configured for your domains. Any mail sent from your Exchange servers should be covered by your authentication records.
• Check your send connectors for any third-party relay configurations that might need updating.
• Review message size limits if large attachment workflows have changed since your last Exchange update.

Tools like DMARCFlow can monitor your authentication posture and catch configuration gaps that surface during infrastructure changes like this one.

FAQ

When exactly is OWA Light being retired?

Likely August 2026, per Microsoft's Tech Community announcement. The precise date depends on when the relevant Cumulative Update ships. Check the Tech Community post for the latest schedule.

Will users lose email access if we miss the deadline?

Yes. When Microsoft disables OWA Light, users who have not migrated will be unable to access web mail at all. They will not be automatically redirected to full OWA. The Outlook desktop client and Outlook mobile app are not affected.

Does this affect Exchange Online?

No. This retirement applies only to on-premises Exchange Server 2016 and Exchange Server 2019. Exchange Online runs a different codebase.

Does OWA Light affect mobile devices?

The retirement primarily affects browser-based access on desktops and laptops. The Outlook mobile app uses a different protocol and is not affected.