Outlook App on Android Mobile device cannot find mailbox

Last Updated: 6/8/21

Problem:

My company started the switch from on premise exchange servers to Office365. My mailbox is still on premise, but my Outlook mobile app on Android stopped working. Could not find my mailbox at all.

Solution:

I tried many things. I am not sure why it is not easier to view the logs.

Remove the account from Outlook for Android
I logged into my exchange server control panel https://exchange.company.com/ecp and use my partial admin rights to location my mailbox and open the mobile device list.
I deleted "Outlook for Android" from the device list. waited a few minutes. it automatically showed up again.
Added my account back to Outlook for Android
Everything worked again.

Also, if you get error 500 "Mailbox not found", then your mailbox may be on premise and you are trying to view your email via office.com or outlook.office.com, which won't work until after your mailbox is moved to the Microsoft365 cloud.

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