This manual refers to an old version of CodeTwo Office 365 Migration. Go here if you use the latest version.

Troubleshooting server connection

No matter if you configure the EWS connection to a source Exchange Server or to a source/target Office 365 tenant, the first action (test) performed by the program is always checking the connection to your server (Exchange Server, as shown in Fig. 1., or Office 365). During this operation, the software tries to access the mailbox of an admin account provided in the previous step of the wizard. If the program cannot connect to your server (Fig. 1.), click the Details link on the right side of the configuration wizard to see more information.

Office 365 Migration EWS wizard failure
Fig. 1. Failure to connect to source Exchange Server.

Study the examples below that show the most common server connectivity issues:

The request failed. The remote server returned an error: (401) Unauthorized.

The error message is produced when the wrong target server administrator account has been chosen, the admin account is not mailbox-enabled (doesn't have the necessary license assigned that includes the Exchange Online plan, in case of Office 365), or the admin's email address is different than its UPN (User Principal Name). You must make sure that provided credentials are the right ones and that they match the UPN. If you are still using the pre-Windows down level logons (DOMAIN\user) you must create a UPN for the purpose of the migration.

This error may also appear when configuring a connection to Office 365 by using an account that has multi-factor authentication (MFA) enabled. Enter the app password instead of your regular Office 365 password when providing the admin account credentials. You can also disable MFA for that account or use another account that is not MFA-enabled. Read more about managing MFA for Office 365 users.

The request failed. The underlying connection was closed: An unexpected error occurred on a receive.

The reason you experience this problem is that you might be using the software version that does not support TLS 1.2 and is therefore not able to connect to Office 365 services. Make sure you have the latest version of CodeTwo Office 365 Migration installed (click the Check for updates link on the Dashboard tab to check that). Read more about problems related to the old TLS protocols and how to troubleshoot them

The request failed. Unable to connect to the remote server.

This error occurs if the domain name in the administrator's email address is misspelled or the password is wrong. To fix the problem, go to the previous step of the connection wizard and make sure to enter correct credentials. A similar message is also shown if the EWS URL is wrong. In that case, go to the first step of the wizard and enter a correct EWS URL.

The request failed. The remote server returned an error: (403) Forbidden.

The error message is produced when there is a problem connecting to the source/target server. Make sure you provided the right name or IP address of the server and the right EWS server address. To check this, you can copy-paste the EWS server address (EWS URL) from the program's settings into your web browser when you are logged in to the source server. If you don't get a credentials request pop-up window, this might mean that you provided wrong EWS server URL or IP.

The Autodiscover service couldn't be located.

There may be a few reasons for this error to occur. If you recently added/migrated a domain the simplest solution would be changing the email address of admin account you are using (in Exchange options on Office 365) back to <yourdomain> The other reason may be that your domain is not yet registered/verified with Microsoft's DNS or there is a problem with the Global Administrator account on Office 365 that is being used with our program. We recommend either checking the domain registration status, contacting the Microsoft Office 365 Support or trying the universal solution below:

  1. Choose a different existing account or create a new account on Office 365.
  2. Make sure the account is fully mailbox-enabled, i.e.:
    • Log in to OWA 365 with this account’s credentials.
    • Set the regional settings if prompted to do so.
    • Send an email to yourself or to another account and confirm it was delivered.
  3. Assign the Global administrator role in Office 365 to this account.
  4. Use this new account in our program.

If the above does not help consider:

  • running the software on a different machine – this way you will rule out problems caused by security settings on the original machine, e.g. firewall;
  • installing the software outside of your environment (forest), e.g. on a virtual machine with trial Exchange Server, at home – this way you will rule out problems caused by customized or even improper DNS, proxy or routing configuration.
The SSL certificate could not be checked for revocation. The server used to check for revocation might be unreachable.

The program is unable to check whether your Office 365 SSL certificate is still valid or not. As per this Microsoft article, this issue is usually related to network connectivity problems. It may also be caused by other factors, for example problems on the certificate revocation list provider side. The solution may involve:

  • making sure your computer has a good Internet connection;
  • waiting an hour or so before trying again to rule out the temporary network problems of 3rd parties;
  • running the software on another machine to rule out any particular machine limitations, network security issues, network settings, etc.
Account mismatch.

This error informs you that the program has found a conflict with the admin account's ID – used credentials no longer connect to the same environment as previously. This is a security measure that prevents any problems that may occur due to changes made in your source or target environment. Once you receive this error, you will not be able to continue with the migration process (including running Rescan), refresh email addresses or reset the migration state. To fix the problem, you need to reconfigure the source and/or target connection by using new admin credentials (with different UPN / email address) that will allow you to connect to the desired server.

This error is most likely to occur after changing the domain on the source and/or target server This especially applies to the situation where you have transferred the domain from the source server to the target server – the existing source connection might connect to your target server instead. The program also detects if you have deleted the admin account (used previously in the program) on your server and then created a new one, with the same UPN / email address. Such an account will be recognized as a new mailbox (as it has a different GUID) and migrated from scratch (and consume another license) in the program. In case none of the above situations took place and you still want to use the same admin credentials, contact CodeTwo Support.


When configuring connections to your Office 365 tenants, we recommend using an admin's account primary email address from the * or * domain, assigned to you by Microsoft. That way no conflicts will occur when you change the domain names on your tenants. Learn more.

Unable to perform this command. Mailbox does not exist

If you receive this error, consult this Knowledge Base article for more information.

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