I am receiving an error during mailbox migration (on-premises exchange2016 to online exchange ).

Question

I am receiving an error during mailbox migration (on-premises exchange2016 to online exchange ).

Damaris Alves Duarte 0

I have an on-premises email server, Exchange 2016 Version 15.1 (Build 2507.6).

I am experiencing issues migrating mailboxes both to the cloud and from the cloud back to the on-premises email server. I identified a migration advisory (https://admin.cloud.microsoft/?source=applauncher#/servicehealth/:/alerts/EX1226910), however, it does not apply to our environment because we do not have multi-geo tenants.

I validated the Microsoft Exchange Server Auth Certificate, and it is not expired — it is valid until 07/09/2030.

Command: Get-WebServicesVirtualDirectory | fl Name,MRSProxyEnabled

Output:

Name            : EWS (Default Web Site)

The Test-MRSHealth command returns without any issues.

This problem has been occurring since January. We noticed it when attempting a new migration on January 26, and since then we have not been able to perform any migrations.

I have hidden the company domain in the logs by modifying it to mail[Moderator note: personal info removed] /EWS/".

Erro: TimeoutErrorTransientException: The call to [Moderator note: personal info removed] timed out. --> The request channel timed out attempting to send after 00:00:07.9177680. Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout. --> The HTTP request to '[Moderator note: personal info removed' has exceeded the allotted timeout of 00:00:07.9177680. The time allotted to this operation may have been a portion of a longer timeout. --> The request channel timed out attempting to send after 00:00:07.9177680. Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout. --> The HTTP request to '[Moderator note: personal info removed] ' has exceeded the allotted timeout of 00:00:07.9177680. The time allotted to this operation may have been a portion of a longer timeout.

2 answers

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Answer 1

Hani-Ng 8,470 Microsoft External Staff Moderator

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Hi Damaris Alves Duarte

Thank you for reaching out to the Q&A Forum with detailed logs and your validation steps.

Based on the specific error signature (timeout at 00:00:07.9) and your confirmation that the MRSProxy bindings are missing from the web.config file, I would like to share some information from my research and my understanding that I hope will be helpful that

Even though Get-WebServicesVirtualDirectory shows MRSProxyEnabled as True, the underlying configuration file (web.config) does not contain the necessary WCF (Windows Communication Foundation) bindings. Without these specific bindings, the server reverts to the default web connection timeout (approx. 8 seconds) rather than the extended timeout required for mailbox moves.

This behavior frequently occurs after installing an Exchange Cumulative Update (CU) or Security Update (SU), which can overwrite configuration files and revert them to a default state.

You can try to force Exchange to regenerate the missing XML blocks in the web.config file and try to run

Disable MRS Proxy:

Get-WebServicesVirtualDirectory | Set-WebServicesVirtualDirectory -MRSProxyEnabled $false

Reset IIS: (Required to unload the current config

iisreset

Re-enable MRS Proxy: (This triggers the rewrite of the web.config)

Get-WebServicesVirtualDirectory | Set-WebServicesVirtualDirectory -MRSProxyEnabled $true

Reset IIS:

iisreset

After running these commands, if you open the web.config file at C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\exchweb\EWS, you should now see a section named <binding name="MRSProxyBinding">. The migration should now proceed past the 7-second mark.

You can see the following Microsoft Learn article regarding enabling the proxy and how updates affect configuration files: Move mailboxes between on-premises and Exchange Online organizations in hybrid deployments

Additionally, please note that because Exchange Server 2016 is no longer supported as of October 2025. Your current installation is running a 2022 build, which leaves the environment vulnerable to newer threats. I recommend prioritizing this move to Exchange Online to ensure your data is protected by modern security standards.

I hope this information proves helpful!

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.

Damaris Alves Duarte 0 Reputation points

2026-03-03T12:10:22.08+00:00

Thank you for your response. I followed the procedures according to your guidance, but unfortunately the "MRS" binding still does not appear. Additionally, the file dates remain unchanged, which indicates that no changes were applied.
Damaris Alves Duarte 0 Reputation points

2026-03-03T23:58:57.7+00:00

I would prefer to recreate the cloud connector. What steps should I follow?

I found the documentation: https://learn.microsoft.com/pt-br/exchange/decommission-on-premises-exchange

However, it assumes that I will decommission the on-premises Exchange server, which is not my goal. The purpose is only to reconfigure the hybrid communication.
Hani-Ng 8,470 Reputation points Microsoft External Staff Moderator

2026-03-04T10:52:15.17+00:00
Hi Damaris Alves Duarte

Thank you for your update!

Since the file date didn't change, it looks like local server permissions or security software might be blocking PowerShell from updating the file automatically.

Here is workaround you can consider that because the error specificially says "Increase the SendTimeout value on the Binding" - the MRSProxyBinding section is missing. You can fix this by pasting the XML block below directly into your web.config file (inside the <customBinding> section) using Notepad as Administrator:

<binding name="MRSProxyBinding"> <textMessageEncoding> <readerQuotas maxDepth="32" maxStringContentLength="5242880" maxArrayLength="104857600" maxBytesPerRead="4096" maxNameTableCharCount="16384" /> </textMessageEncoding> <httpsTransport authenticationScheme="Negotiate" maxReceivedMessageSize="104857600" /> </binding>

(Don't forget to run iisreset after saving).

Decommission on-premises Exchange" documentation: According to my understanding, that guide is for permanently removing your server after a migration is 100% complete. Using it now will delete critical attributes and break mail flow for your users.

To "recreate" or "refresh" the connectors without breaking your environment, you must use the supported wizard. (For detailed information: Hybrid Configuration wizard | Microsoft Learn

If the wizard runs successfully but the 7.9-second timeout persists, this confirms that your Server OS or Antivirus is locking the web.config file. In that case, the Manual XML Edit (shared in the previous email) is the only way to support this the issue.

Additionally, please note that Exchange Server 2016 reached End of Support on October 14, 2025. Since your environment is no longer receiving security updates, I strongly recommend resolving this blocker quickly so you can move your data to the supported Exchange Online platform.

I hope this helps!
Hani-Ng 8,470 Reputation points Microsoft External Staff Moderator

2026-03-05T06:06:01.7466667+00:00

Hi Damaris Alves Duarte

I just wanted to follow up to see if you have any updates or need any additional information. Please feel free to let me know!
Damaris Alves Duarte 0 Reputation points

2026-03-05T19:34:36.4333333+00:00

Hello, unfortunately it seems the problem worsened after I removed the endpoint that existed in Exchange Online.

Now when I try to run the Hybrid Configuration Wizard (HCW) I receive the error HCW0 - Bad Data (screenshot attached). I can also provide the logs, but since they contain a lot of information about our company’s email environment, I will only share them if I can send them through a private link.

Also, I added "MRSProxyBinding" to the web.config file as suggested and ran iisreset, but it did not resolve the issue. I have been receiving the HCW0 - Bad Data error since the moment I removed the cloud endpoint, which was on 03/03/2026.

I also attached a screenshot showing my attempt to manually create the endpoint in the cloud using PowerShell. The command returned success, but when trying to move a mailbox using the newly created endpoint, an error occurred.

There is also a screenshot showing my attempt to create the endpoint directly from Exchange Online, but it returns an error without any details.

I tried these alternatives because when running HCW, it presents the error described above.

I am very grateful for your support and hope this issue can be resolved soon.

Answer 2

Damaris Alves Duarte 0

The web.config file located at C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\exchweb\EWS does not contain bindings with the name MRSProxy.

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I am receiving an error during mailbox migration (on-premises exchange2016 to online exchange ).

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