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I have a really strange one... we formerly had our tenant set up to grant E365 Plan 1 and Azure Plan 1 licenses to all mail enabled users, and have for a while. Employees granted mobile access were allowed to connect to their mailboxes with their phones, and we had not yet moved to restricting it to "approved" mail clients (although it is on the short list).

This weekend we changed all of their licenses to M365 Business Premium licenses, and all of a sudden I have multiple users who cannot access their mailboxes from native Android or iOS mail clients. In each case I've looked at, installing Outlook solves the problem, but until I've communicated the change, I want to continue to support native mail clients. The only thing that changed to trigger the issue is the change of licensing... is there something missing in the Business Premium license that the Exchange Plan 1 license had? The audit logs show successful login, they just get client errors akin to "Cannot verify account".

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Office 365 Premium got more security behind it.

As it include Entra I would make sure the MFA was not forced on all your user in the verification's phase, and you have conditional access too (depending on the region it can impact the login)

Try to login to office.com website from one of those tablet in error to see if it ask a verification's method or to see a more complete error message. If it ask for a verification method, it will be to complete before retrying to configure the mail's client.

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  • We've been using Entra since our move to E365... and we have conditional access and MFA enabled. The login logs for these users show success, and MFA is completed correctly as well. If I reset the user's sessions via the Entra portal, they are re-prompted properly for 2FA and it also shows success. It just fails to "verify the account" when it gets to the Exchange level... it is very strange, almost as if there is a client app verification happening even though that is not part of our conditional access at all. Thanks for replying though. Commented Jun 18 at 1:00

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