Outlook prompts for password when connecting to a secondary or archive mailbox

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Fix for Outlook 2016, 2019, 365 prompting for a password when adding a second mailbox in Exchange Online, when the primary mailbox is still on-premises.

A common issue when migrating to Office 365/Exchange Online from on-premises versions of Exchange is users being prompted for passwords when connecting to a second mailbox hosted online, when their mailbox is still hosted on-premises.

This can happen in these scenarios:

In this case, Outlook will prompt for a password when trying to connect to the online mailbox.

  • HKEY_CURRENT_USER\Software\Microsoft\Exchange
  • New, DWORD Value.
  • Name: AlwaysUseMSOAuthForAutoDiscover
  • Value: 1

See the following Microsoft article for more information:

Outlook prompts for password when Modern Authentication is enabled

Posted in Exchange Online, Office 365

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