Microsoft has told IT administrators that IE Mode in Microsoft Edge, which is the final method of running the Internet Explorer engine on modern Windows, will be discontinued by the end of 2029, as stated in a message on the Microsoft 365 admin center.

Although Internet Explorer 11 was retired many years ago, its engine is still in use via IE Mode. The company is advising organizations to start migrating the legacy applications that still need Internet Explorer at this time, since some modernization projects can take several years.

Microsoft has stated that it will give a new end-of-support notice at least one year before the actual date.

Support for Internet Explorer was withdrawn by Microsoft more than ten years ago, but the browser still remains in current versions of Windows via IE Mode, and IE Mode together with the engine technology used by Internet Explorer will no longer be available by the end of 2029.

Microsoft has sent a message through the Microsoft 365 admin center (MC1473151) to remind organisations of the planned retirement. Firstly mentioned in 2021, IE Mode in Microsoft Edge will be supported "at least" until the end of 2029, and the company will publish a new end-of-support notice at least one year in advance.

The reason given for sending these regular deprecation reminders is that it can take years to migrate the legacy applets, apps, and applications which still need Internet Explorer.

IE Mode is a compatibility feature in the more recent versions of Edge and is based on Google's Chromium browser engine, allowing web pages to be displayed using the Trident engine associated with Internet Explorer 11, a engine also known as MSHTML, which is the proprietary layout engine that was first introduced with Internet Explorer 4.0.

Internet Explorer 11 is based on MSHTML 7.0 and supports WebGL applets as well as the now-discontinued SPDY web communication protocol; those organizations which do not make use of any IE-based applets need not take any action when Microsoft issues the MC1473151 alert.

Even though IE Mode will likely continue working with few issues after 2029, Microsoft asks organizations to prepare now:

1. Evaluate the IT infrastructure to identify those elements which are still necessary to run in IE Mode from the point of view of the business and its missions.
2. Refresh, reupload, replace or reconstruct those applications and websites using modern web technologies.
3. The App Assure service offered by Microsoft can assist eligible customers in checking and improving the compatibility of their custom applications with the newer Windows platforms.

Microsoft cautions that "if you plan ahead your organisation will be able to identify migration risks and will manage the chance of disruption when you are moving away from dependencies on IE mode."

IE Mode will continue to be supported at least until the end of 2029, Microsoft promising a one-year advance notice before the end of support is finally reached.

Organizations that have no dependencies on IE should take no action, but those who rely on legacy IE applications are advised to start making arrangements for migration at this time since modernization can be a lengthy process.