Hi @NurHossain-4331 ,
1. Is there a firewall between the Exchange servers? If so, please communicate with the firewall team to ensure that all ports required by Exchange have been opened and the firewall's security policy will not affect the communication between Exchanges. And make sure there is no NAT rule on it. If possible, turn off the firewall temporarily.
2. Please try to remove the server that the cluster service isn't starting on from the DAG and go to the server itself and run "Clear-Custernode" from PowerShell. Then re-add the server to the DAG and see if the issue is resolved.
3. You could run the following command to check the real-time status information about DAG:

 Get-DatabaseAvailabilityGroup <> | Format-List

In addition, are there any related error logs in the event viewer? If possible, please provide detailed error information, but please note that please cover your personal information.

Hi @AmitBadgujar-7293 ,
I am writing here to confirm with you how thing going now? If the above suggestion helps, please click “Accept as answer” to mark helpful reply as an answer.Your action would be helpful to other users who encounter the same issue and read this thread.
Thanks for your understanding.

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Hi @ElazaraArbiv-2263 ,
Thanks for the information.

1.If you want to view the complete information of the error event, you can save the event log and open it in the server where the Exchange server is located.

2.It is normal that an error event message with event ID 6 appears in MSExchange Management. Because the event message will appear when you run the command line and fail, but this does not mean that there is a problem with the function of your Exchange server.

In addition, the Exchange Admin center is a tool for managing the Exchange server on the interface, but the operation is actually running cmdlets in the background. Therefore, when an error occurs during an operation in EAC, the corresponding error event will also appear in MSExchange Management. For example, when creating a new user mailbox, the address of the newly created user mailbox already exists, and the creation fails. An error event with Event ID 6 will be created at this time.

So if your Exchange server is working normally, you can ignore the error event. Because this event cannot be used to determine that there is a problem with the normal operation of the Exchange server.

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Hi @BrianZhang-6206 ,
I am glad to know that the above information can help you.

Have a nice day!

Hi @Bossieman-7030 ,
I am glad to hear that your problem has been resolved, and thank you very much for the solution you shared.

If you can, you can mark your solution as an answer to help users in the community who have the same problem. This will help more people.

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Hi @RaymondSupilanas-4061 ,
According to the error information:
1.Please make sure that your account have correct permission:
Please refer to: Prepare Active Directory and domains for Exchange Server

2.About the error message "The Mailbox server role isn't installed on this computer."

Please run the following command to make sure that your computer is the mamber of the same Active Directry domian and site as the schema master.

 netdom query fsmo

3.About the error messag "An unsupported operating system was detected. Exchange Server 2013 Client A
ccess, Mailbox, and Edge Transport server roles support Windows Server 2008 R2 S
P1 or later and Windows Server 2012." and "Visual C++ 2013 Redistributable Package is a required component."

Please make sure that your AD and windows version meet the requirements, and make sure all prerequisites are installed.
Please refer to: Exchange 2013 prerequisites and Exchange Server supportability matrix

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Hi @RaymondSupilanas-6595 ,
Due to environmental constraints, I have not tried an upgrade specific to Exchange 2013 to Exchange 2019 in a hybrid deployment. But according to my other upgrade practices, and studied similar cases and articles. I think you can follow the steps in the link provided above to upgrade.
But it should be noted that during the upgrade process, please ensure that your environment meets the deployment of Exchange 2019.
For more information: Exchange Server prerequisites, Exchange Server system requirements and Exchange Server supportability matrix.

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Hi @NurHossain-4331 ,
In addition to the above, the following points need to be confirmed:
What's the version of Exchange server?
Have any changes been made to the Exchange organization before the problem occurred?
Please check the Authentication of MAPI,EWS and ActiveSync in IIS.

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Hi @RudolfAmarlapudi-2729 ,
It’s been a long time no receive your reply. I am writing here to confirm with you how thing going now?

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Hi @RogerRoger-2394 ,
According to my test, if you create a transport rule in on-premises Exchange server, it will not sync to Exchange online. You just need create this transport rule in Exchange online.

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Hi @ThopulouD-3208 ,
Based on my research and test, the "PR_CONTENT_COUNT" parameter represents the number of mails in your Outlook local data, that is, the mails you can see directly when you first open the folder. Since MFCMAPI checks the mailbox information through Outlook profile, I think this does not include server-side mail.

The number of Items in the lower right corner represents the number of all mails in the folder, including the server-side. According to my test, I set "Download email for the past" to three days. When I opened Outlook again to log in to the mailbox, I found that "Items" showed the number of all messages. When I click "Click here to view more on Microsoft Exchange", I can view the server-side mail in the folder, but " PR_CONTENT_COUNT " is still displayed as 0.

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Hi @ThopulouD-3208 ,
According to my viewing of Outlook using MFCMAPI, I found that the value displayed by the parameter "PR_CONTENT_COUNT" is the same as the number of items in the folder, and when I remove the mail from the corresponding folder, the value of this parameter will change immediately.

In addition, since the forum is a public platform, in order to avoid exposing your personal information, I will help you remove the first screenshot you provided.
Thanks for your understanding.

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Hi @ThopulouD-3208 ,
According to the Microsoft's official article you provided, we could know that setting the MDB_ONLINE flag in the ulFlags parameter to override the connection to the local message store and open the store on the remote server. Since the connection with the local data file has been disconnected, all emails will be retrieved from the remote server. I think this is the same for Online mode and cache mode. So the load on the remote server is the same.
But for the daily use of your mailbox, Outlook will first retrieve the mail in the local data file, which will reduce the load of the Exchange server.

This is normal for your customers. As I mentioned above, according to your customer's settings, only nearly one month's mail is synchronized to the local Outlook data file. Earlier emails will need to click on "Click here to view more on the exchange" to connect to the Exchange server to retrieve them and view them.