Outlook cannot connect to the mailbox. Hybrid

Question

Hi. Exchange 2019 on-premise. Last CU last SU.

Office 2019 LTSC Pro Plus.

For the last week, Outlook cannot connect to the box that is in Office365.

How to diagnose this ?

AAD synchronizes successfully. The Hybrid Setup Wizard completes successfully. There are no problems with local mailboxes.

Answer 1

@Андрей Михалевский

Glad to see this issue is solved. Bue to the change of Q&A policy, the question author cannot accept their own answer. They can only accept answers by others. Here is a summary about this thread. You could accept it as an answer. It could be beneficial to other community members reading this thread.:

1. Logon OWA to make sure using the correct account and password.
2. Use "Test Email AutoConfiguration" to check the Autodiscover lookup step for migrated mailbox.

About Autodiscover lookup steps, we could follow this blog: Office 365 Autodiscover Lookup Process

Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.

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Answer 2

Please check the Outlook connection status using the tray icon (https://learn.microsoft.com/en-us/outlook/troubleshoot/connectivity/description-of-the-connection-status-dialog-box):

1) Press and hold Ctrl, and then select the Microsoft Outlook icon in the notification area. (the Outlook icon can be hidden from view in the notification area)
2) Select Connection Status.

It should give you a clear idea what's wrong. If you cannot solve it by yourself, feel free to post it here.

Answer 3

Outlook is a standalone application that periodically attempts to connect to the mail servers. It works by fetching all the emails into local storage and letting you view emails from your computer. However, this might not work if the application itself can’t connect. Here are some of the reasons why this might happen:

• Bad internet connection
• Account corruption
• Corrupt data file
• Corrupt Office Installation
• Outdated Application

Below are some solutions you can try to resolve this problem:

• Checking Internet Connection
• Turning Off Work Offline
• Repairing Outlook Account
• Disabling Extensions
• Rebuilding Outlook data file

If the reply helped you, please remember to accept as answer.
If no, please reply and tell us the current situation in order to provide further help.

Answer 4

@Андрей Михалевский

When using the "Test Email AutoConfiguration", you need to uncheck the "Use Guessmart" and "Secure Guessmart Authentication", only check the "Use AutoDiscover". Remember to remove privacy Information (Such as domain name) before posting.

I want to confirm with you that is this mailbox migrated to Exchange online or created on Exchange online?

Did you try to log in Exchange online OWA (https://outlook.office.com/mail/), whether this mailbox could be login OWA successfully? The migration operation may change email address to Exchange online default email address, so it is suggested to try to login OWA first.

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If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

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Answer 5

I discovered the problem. The Proxy adress in internet explorer was configured incorrectly.