How To: Importing PSTs Files in Office 365

Import PST Files to Office 365


PLEASE NOTE:  There is a change in this program.  By default if imports into the Root of Mailbox.  If that is not what you desire please change the settings accordingly.


To Import PST Files into Office 365 choose the Import PST Files option on the main screen and click Next.


On the next screen you will be prompted for your Administration Credentials for Office 365.  This account must have a mailbox.


  • If the user Classic Interface is selected the PowerShell endpoint is  If deselected the the end point is
  • If the Show Mailbox Size checkbox is selected, it can take much longer to load the list of mailboxes.
  • Filter Get-Mailbox request is used primary for selecting the Select DiscoveryMailbox only.  In other uses it can be used as a filter.  For example, PrimarySMTPAddress -eq ''.
  • In larger organizations you can use MAPI to Get Mailboxes from the GAL instead of Remote PowerShell.  Checking this option results in a small performance improvement.
  • If you have a license key for over 1000 users, you can skip Getting All Mailboxes via Remote PowerShell.  You will then have to search for the mailboxes or use a CSV file on the next screen.

Basic Migration

The example below will describe a basic migration and then we'll get into more advanced migrations. 


So Step 1 is to select the Import Source.  There you will presented with a Select PST File, which will allow you to select a PST.


Next you'll want to choose the Destination from the Select Mailbox screen.


Next you'll want choose where it goes. The Mailbox is the root of mailbox and the root is the top level of this mailbox.  So this will place all items in the same location as they were the source mailbox.  If you were to choose Archive, they would be placed in the same place in place in the Archive.  If you chose PST name this would create a PST Name (based on the name of the PST file that exists in the archive) in the folder specified.


Next click the Add to Import Queue.  You can repeat this process for users.  Then click the Start Import button to start the import.

Advanced Migrations

CSV Import

If you want to import a list of PST files, the format for the .csv is simply:

When using the CSV option your CSV file needs a valid header row

An example of a csv with a valid header row should look like


Valid header rows

Pstfilename : Path to the PST you are importing
SourceMailbox : Used when importing from On-Premise Exchange
Destination : Primary SMTP address of the Mailbox you are importing to
Usepstrootname : If true a subfolder will be created to import into otherwise false mailbox root will be used
Useaddressrewrite : if true Address rewriting will be used (enabled by default)
Dontimportdeleteditems : if true deleted Items will not be imported
excludefolders : contains folders to exclude for the export separated with a ; eg \Inbox;\SendItems;\Contacts
excludesubfolders : if true the subfolders of the exclude folder will be excluded as well
includefolders : contains folders to Include in the import separated with a ; eg \Inbox;\SendItems;\Contacts
includesubfolders : if true the subfolders of the include folder will be included as well

Select a History File 

The History files are good if something goes wrong with Exchange Migrator.  You can simply click on the History file and restore the last good know configuration.  This is often times good if the Exchange Migrator if the program expectantly terminates. 

Folder Filtering

Folder Filtering can either be Enabled or Disabled.  If you choose the Select Folder Filter you'll be presented with the following the dialog box.


Here you will enter all the folders you want to Include in export.  Note at the bottom of the screen is a toggle for Include Subfolders of Selected Folders.  On the Exclude screen you would simply enter the folder you wanted to Exclude from the export.

From Mailbox

If you choose the From Mailbox you'll be presented with a Folder Filter button. 


Here you will enter all the folders you want to Include in export.  Note at the bottom of the screen is a toggle for Include Subfolders of Selected Folders.  On the Exclude screen you would simply enter the folder you wanted to Exclude from the export.

In both of these examples, you should notice the PST File decreasing it's number of items.


Skip Deleted Items

This setting excludes importing the Deleted Items folder in the PST and any sub folders in this folder.

Import Options

Upload Options

Use MAPI and EWS for Upload

This setting will automatically be enabled or disabled depending on the version of Office 365 you are importing into.  Checking this option will result in the best performance, but sometimes it is necessary to uncheck this option.  By default, it uses both MAPI and EWS for throttling, but sometimes it's necessary to disable MAPI and just use EWS for uploads. 

Use Direct Discover

This setting should be selected if the Autodiscover records aren’t setup for the domain you are trying to import PST files into.  With this setting, the Exchange Migrator will attempt to directly connect to Office 365, bypassing the Autodiscover process.

Use EWS Impersonation

The default is to Use EWS Impersonation, meaning the migrator will impersonate the owner of the Mailbox when uploading items using EWS. Because of the throttling limitation imposed on Office365 this setting is recommended.

Use Throttle Switching

The default is to use throttle switching this controls how the application manages throttling to ensure best upload performance. 

Address Options

Use Address Re-Re-Writing

Address rewriting will rewrite the Native Exchange email address format (for example EX: /o=First Organization/ou=first administrative group/cn=Recipients/cn=UserName’) which are only valid in the source Exchange organization to the SMTP address for the address entry if it can found within other message properties or resolved by looking at the Global Address List based on the Display Name of the recipient. Note because this is an automated processes exact address matching can never be 100% assured if GAL resolution is used and more than 1 contact has the same display name.

Import Auto Complete (Mailbox Only)

Re-writes contact information for mailboxes migrated to Office 365.


Auto Grant Full Mailbox Access 

Should be enabled by default.

Skip Auto Remove Access

Should be disabled by default.  If there is change where the Administrator account already has full control over the mailboxes this account step can be stopped.

Error Processing

Ignore Single Property Errors

By default this is enabled.  This allows the Exchange Migrator to migrate any items that have a single property error.

Don't Save OverSize Messages

By default that setting is disabled.  This allows the Exchange Migrator to not save any oversized messages.

Duplicate Detection

The Custom Id (Best) option should be used if you are importing a static set of PST files using the Exchange Migrator.  This will prevent duplicates if the exact same PST file is imported multiple times into the same mailbox.  Note, exporting a mailbox more than 1 time to different PSTs will result in duplicates if this option is selected.

The SourceKey option uses 3 different keys for duplicate detection.  It first tries the PSTid, then it uses the SourceKey and then the SearchKey. The SourceKey and SearchKey should the be same on multiple copies of an the Item, so if this is used it shouldn’t import a message if it finds a match for either of these three keys. This should prevent duplicates in the instance where an aborted Outlook import has been performed and you want to use the Migrator.


If checked you can specify an email address to send notifications to when operations complete or fail.

Thread Control

In most cases these shouldn’t be modified, but here is what these settings control.

Max Threads – The number of simultaneous TCP connections to Exchange.  The Exchange server will throttle any more than 10 simultaneous connections.

Batch Size – The total number of message that will be sent in one batch.  The actual batch size will depend on the size of the messages in the batch.

Running the Import

The import queue will look similar to that below.


The log file link is in the upper left.  That log will be the log that you send to Kaseya if you should need it.

The Error Count is the total count of errors and the OverSize Count is the total number of oversized items.

There are some stats about how fast the migration is going.



Updated: April 16, 2016

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