How to tackle Office 365 Migration Errors & Troubleshooting?

Man sitting at a laptop trying to solve migration errors

Office 365 and Exchange Server are both complex products so to establish connectivity and migrate your mailboxes it’s probably not surprising that errors can occur.

We take a look at some of the common Office 365 migration issues you may see during or when setting up your mailbox migration to Office 365 using Exchange Web Services (EWS) based products.

With any form of mailbox migration, the first errors you are likely to come across are initial connection problems when linking to your source and destination email servers, and whilst Exchange Web services (EWS) migrations are probably the most complexity free migration method we still see a few issues.

How to fix these most common Office 365 Migration issues?
How to fix these most common Office 365 Migration issues?

1) Connection Issues

Exchange Web Service (EWS) as it’s name suggests requires web (http or https) access to establish a connection between the source and destination services. This service is always available on Office 365 and generally available on most Microsoft Exchange installations.  On the destination with office 365, this is relatively straight forward using but the source servers, unless office 365 as well, things can be a bit more complicated.
Interesting, but true. The majority of connection issues we see are related to error when entering details. Click To Tweet
A cut and pasted URL can have a space character accidentally in front or behind of it or a comma instead of a dot are common forms and can delay progress while the issue is isolated. Also, user permissions with insufficient or no rights to access a mail server can equally delay progress. We suggest using two methods to make sure you are in the right place and connecting with the correct permissions and therefore reduce time spent with any office 365 migration troubleshooting.

Logging in to webmail using an admin or users account, creating an email and searching for the required user using the login email id will tell you quickly if the user can be seen. If the user doesn’t show up, then and EWS based migration system will not see the mailbox to migrate.

Also, available is a tool provided by Microsoft for testing EWS connections. This tool allows you to enter the details of your mailbox server and it will then test to make sure the server is fully available. Microsoft’s  remote connectivity analyzer can be found at

Below you can see the option for testing connectivity for Microsoft Exchange web services.

Microsoft Remote Connectivity Analyzer Tool for testing EWS Connections
Microsoft Remote Connectivity Analyzer Tool for testing EWS Connections

2) The specified object was not found in the store

The mailbox may have been hidden from the Global Address List. This can be checked if you have administrator access to the system by checking the “Exchange Advanced“ tab within Active Directory Users and Computers.

If you don’t have administrator access, you can check if the user is hidden by searching within the Global address book from another user account or by using outlook or webmail (OWA). If the user is hidden it will not appear when you search.

This error may also occur if there is a folder containing a backslash \ character. In this case, replace the backslash character with something different for example a dash – .

The folder permissions that the object is in (accessed by right clicking on the folder within outlook and selecting properties then permissions) have been altered and possibly locked down to specific users. Please make sure they are the same as all other folders and have no restrictions in place. Admin accounts used for the migration with insufficient privileges may also cause this error.

3) SMTP address has no mailbox associated with it

Most of the time this issue relates to an error when typing in the username for the mailbox to be migrated. However, if this error may also occur for the following reasons.

If for some reason the account is not visible within the address book Exchange web services based migration tools will not see the account to be migrated. This can be tested by logging into webmail (OWA – Outlook Web Access) with a user or administration account. Then creating a new email and then entering the users email id into the “To” field. If the address resolves to an existing mailbox in the address book, then it will appear in a provided list which is the correct response. If, however it fails to appear in the address book then it will not be seen.

If using an admin account within office 365 it’s possible that a license has not been assigned. As with all office 365 changes, please allow time for any changes to propagate.

4) Server cannot service this request right now

At times of high load or large amounts of data movement you may experience throttling and a rejection of the request to move data may occur. This occurs to protect services like Office 365 from being overloaded as the alternative is a total outage of the service.

There are several things you can do to avoid throttling and to maximise the amount of data you can migrate in any time period.

Connecting to Office as a user or using impersonation as an admin user allocates the resource used across multiple user accounts and will increase the amount of data throughput that can be completed.

If possible, avoid peak usage times by carrying out your migration outside office hours or at weekends.

Also, it is worth contacting Microsoft and explain you are carrying out a migration and could they minimise the amount of throttling being carried out on your tenant account. 

Microsoft will usually give you 90 days of reduced throttling to complete your migration without an office 365 migration stuck on syncing. Click To Tweet

5) Unable to connect to the remote server

This issue is most likely to be related to Throttling or server performance.

If you try to log in using webmail then this usually works correctly but connecting to EWS for migration purposes displays one of these errors.

The most common cause of this error is a configured parameter preventing the server from accepting the connection or poor performance of the server. You get the error Server Busy from the Exchange Server and the connection is refused. Give it a go again at a different time and you may be more successful.

If not server performance related, then it is usually server settings that create these errors and can be resolved by removing restrictions on the server.

The account does not have permission to impersonate the requested user. If impersonation is not enabled when using an admin account on Office 365 or exchange to access mailboxes you will receive this error. To enable the required permissions requires a couple of easy commands to be carried out using Powershell and permission with then be allowed. You can find articles on how to do this in our 
Migration Monster knowledge base.

6) 401 Unauthorized

The login details used to access the mailbox are invalid, or the login details specified do not have access to the configured mailbox, or you may have over utilised resources on the email server.

This error is mostly caused by the user name and password specified not being able to access the mailbox. Please verify if the user name and password are correct by attempting to log in to the user’s mailbox using webmail. If you are connecting using administration level access, make sure to log in to the mailbox using administrator username and password because this is how EWS will access the email systems.

If you have verified that the credentials are correct, try re-entering the credentials as sometimes hidden space characters can cause problems.

Check to make sure the account you are using to authenticate is not waiting for a password change by logging in to webmail/office 365 using the account details.

If using email address format for user login, make sure that the UPN (User Principal Name) matches the primary email address for logging in.

If you have eliminated user login issues from your investigation, it is also possible that insufficient resources could be the cause.

If migrating to or from Office 365 and using as the destination/source URL to connect then try using instead. We would also suggest trying to connect again outside office hours when the Office 365 service is less heavily used.

For on premise servers, issues like poor CPU performance, low memory levels, high disk utilization and network issues can all generate this error.

Again, with on premise server’s poor internet bandwidth can also cause this issue. In this instance we suggest reducing the number of concurrent migrations, migrating outside office hours or you will find your office 365 mailbox migration failed, incomplete or you may experience office 365 post migration issues.

Insufficient user permissions for both user level accounts or administration level accounts may also cause this error. 

For assistance with your migration to office 365, please don’t hesitate to get in touch.

Happy Migrating!

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