How to Fix “Transient Error Communication Error Transient Exception has occurred. The system will retry”?

Migration from local Exchange Server to Office 365 can sometimes become a tough challenge if you encounter any errors and issues. Even after making the necessary changes or planning well ahead, you may get errors during migration of mailboxes. Below, we will be discussing an error that occurs while moving mailboxes from the on-premises mailboxes Exchange Server to the Office 365 or Exchange Online in a full hybrid setup. The error message is as follows:

Mailbox Move to the cloud fail with error: Transient error CommunicationErrorTransientException has occurred. The system will retry.

This error occurs when the migration batch is started. The error message is saying that the mailbox failed to move due to communication and it will retry later. From the error message, it seems that the problem is network related. The error message looks quite generic. Therefore, you need to troubleshoot various areas to identify the real cause of the issue.

Solutions to Fix “Transient error CommunicationErrorTransientException has occurred”

As mentioned above, the issue is related to network. There are various areas where you can look for the culprit. It could be a single issue or multiple points in the network which might be blocking the communication between the local Exchange Server and the Exchange Online.

Let’s start from the operating system of the server from where the communication is started. If the Windows Firewall is enabled, you need to confirm that nothing is blocked from it.

You need to first check if the Windows Firewall is enabled. For this, open the Windows Defender Firewall and see if the Domain networks option is enabled.

Next, you need to check the log file. You can find the location of the log file in the Domain Profile properties in the advanced properties.

You can click on Customize and see the location of the log file.

By default, the location of the log file is: %systemroot%\system32\LogFiles\Firewall\pfirewall.log.

Here, you will find all that could be BLOCKED. You can open the necessary ports from the local firewall. If nothing is blocked, then it indicates that the issue is from the server onwards.

If you have a hardware firewall, then check if the HTTP requests are blocked. Most firewalls block HTTP requests. You need to whitelist the server. In case of a perimeter firewall, you need to disable the flooding check and block on the IP address of Microsoft 365 and the local Exchange Server. Since there are various IP addresses for Exchange Online, you need to confirm and get the list of IP addresses from the Microsoft 365 URLs and IP Addresses Range.

In case you have Microsoft Forefront TMG installed as your network traffic management, you need to fix the problem by either increasing the Flood Mitigation limit or whitelist the IP addresses.

Open the management console and expand the Intrusion Prevention System. From there, click on the Behavioural Intrusion Detection and open the Configure Flood Mitigation Settings.

This should allow you to move the data to your Exchange Online with no issues.

There might be multiple points where your traffic can be blocked. So, it’s best to involve your network team or supplier for more information and troubleshooting.

Another option you can try if this fails is to use the MFCMAPI tool on your Exchange Server. Open the MFCMAPI.exe, click on Tools and Options. Here, you need to check the Use the MDB_Online flag when calling OpenMsgStore option and click OK, before opening the mailbox. Next, click on the Open Store to browse the mailbox and try to identify any problematic folders which might have hindered the move of the mailbox.

To Conclude

Hybrid model is an ideal method for migration but it is slow and needs further configurations and setups. As an alternative, you can consider using applications such as Stellar Converter for EDB that can really reduce the migration cost and time. With this EDB to PST Converter tool, you can easily and directly migrate mailboxes and other data from multiple EDB files with no size limit to Office 365 (Exchange Online). You even doesn’t need to have an Exchange Server installed. To ease the migration, it offers features such as automatic mailbox matching and exporting of priority mailboxes first. You can export user mailboxes, user archives, shared mailboxes, disabled mailboxes, and even public folders. In addition, you can granularly export the EDB data to PST and other file formats, and also to another live Exchange Server database.

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About The Author

Shelly Bhardwaj

I am a Product Consultant and is associated with Stellar Data Recovery from last 8 years. I write about the latest technology tips and provide custom solutions related to Exchange Server, Office 365, MS Outlook, and many other Email Clients & different flavors of OS Servers. Read More