Outlook open but not sync

Question

Hello all,

Today I created user in AD then open ECP and create user mailbox as "Existing user" this normally step every day work, but today after created user and setup on outlook not sync anything and I showing something

This attached from user have a problem

and this from normal user

I try remove this user and make it again but the same, also try create test user he working fine.
I check virtual directory internal/external url

Exchange 2016 on-prem

Answer 1

@AHMAD HASSAN

I think the mailbox that you used is an Office 365 mailbox rather than Exchange on-premises mailbox.

To narrow down it, I would confirm below information about you:

1. Do you use a hybrid environment? Whether is this mailbox an Office 365 mailbox?
   
2. Hold "Ctrl" and click Outlook ICO, then check the "Connection Status" (You can post the result after removing domain name)
   
   
3. You can also use "Test Email AutoConfiguration" to check the connection process
   
   

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