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Box for Microsoft Office: Box prompts for login whenever an Office file is opened (Seamless Login)

Issue

When opening a Microsoft Office file, such as a Word, Excel, or PowerPoint file, from Box Drive, users may repeatedly see an authentication dialog asking them to sign in to Box. This dialog is referred to as the Seamless Login pop-up.

This issue may have the following characteristics:

  • Users are prompted to sign in again on a later date, even after successfully signing in.
  • The prompt may appear even for users who do not use the co-authoring feature.
  • The prompt may also appear when Office is launched through Box Edit (formerly Box Tools).
  • The prompt may continue to appear if the relevant setting remains enabled in the Admin Console, even after Box is removed from Connected Services in Office.

Root Cause

This behavior is caused by Microsoft’s Seamless Login feature. Seamless Login has become generally available (GA) for Microsoft Office desktop applications since April 2026.

When “Box for Microsoft Office Co-authoring” is enabled in the Box Admin Console, users may automatically be prompted to sign in to Box when they launch an Office application.

The Seamless Login pop-up appears when all of the following conditions are met:

  1. Office Co-authoring is enabled for the file owner or the tenant.
  2. The “Box for Microsoft Office (Desktop)” integration is enabled for the affected user.
  3. Box has not been added to Office as “a Place or Connected Service”, or the user is not signed in to Box in Office.

The prompt may appear even if the user does not intend to use the co-authoring feature, as long as the feature remains enabled in the Box Admin Console.

Resolution

Depending on whether you use the co-authoring feature, follow the instructions for the applicable case below.

Case A: You want to use the co-authoring feature

Sign in to Box when prompted. After you complete the initial sign-in, the prompt should no longer appear. If the prompt appears every time you open an Office file, verify that Box has been correctly added to Office as a Connected Service.

For Windows:

  1. Open any Office application, such as Word, Excel, or PowerPoint.
  2. When the Seamless Login pop-up appears, sign in to your Box account.
  3. After signing in, verify that Box is listed under File > Account > Connected Services in the Office application.

Case B: You do not want to use the co-authoring feature or see the pop-up

Disable the co-authoring feature in the Admin Console. Currently, there is no end-user setting that can be used to disable the pop-up. An admin must disable the co-authoring feature in the Admin Console.

For admins:

  1. Log in to the Box Admin Console.
  2. Navigate to Integrations > Settings > Box for Microsoft Co-authoring.
  3. Click Edit Configuration.
  4. Under Enable for everyone except select users and groups, add the affected user.

Note: If the “Box for Microsoft Office (Desktop)” integration remains enabled for the affected user, the behavior may be inconsistent. To fully disable the co-authoring feature, you must disable it in the integration settings in the Admin Console. Removing Box from Connected Services in Office alone is not sufficient.

Information

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