Problem transferring outlook data to a new computer

Bernard Gordon 20 Reputation points
2026-08-14T19:47:31.11+00:00

When the Outlook data was loaded into a new computer, every email was transmitted back to the source, how do i prevent this

Outlook | Windows | Classic Outlook for Windows | For home
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2026-08-14T19:47:47.58+00:00

This usually happens when the mailbox is an Exchange, Microsoft 365, or Outlook.com account. In those account types, Outlook data is stored on the mail server, and when Outlook is added on a new computer it syncs mail with the server. The offline cache file (.ost) is recreated automatically and should not be moved between computers.

To avoid sending old local mail back into the synced mailbox:

  1. Check whether the old data came from a .pst file or a server-synced account.
    • If the old mail was in a POP account .pst file, move or import only the .pst data you want to keep.
    • If the account is Microsoft 365, Exchange, or Outlook.com, do not move the .ost file. Outlook recreates it automatically.
  2. If mail was imported from a .pst, import it carefully.
    • In classic Outlook, use File > Open & Export > Import/Export.
    • Import the .pst into the location intended for archived mail, not into the live mailbox unless that is required.
    • If Outlook shows “The source and destination folders for this operation cannot be the same”, rerun the import and choose Import items into the current folder.
  3. If the goal is to keep old mail only on the new PC, keep it in a separate Outlook Data File (.pst) instead of merging it into the server mailbox.
    • Moving a .pst file to a new computer keeps the stored mail, but it does not transfer account settings.
    • After copying the .pst, set up the email account separately on the new computer, then open the .pst there.
  4. If the imported .pst cannot be accessed, check file permissions.
    • Right-click the .pst file, choose Properties.
    • If it is Read Only, clear that setting.
    • If needed, go to Properties > Security > Edit and grant the signed-in account Full control, then restart Outlook.
  5. If using new Outlook instead of classic Outlook, switch to classic Outlook for .pst work. New Outlook has limited .pst support.

For Microsoft 365, Exchange, or Outlook.com accounts, email is already backed up on the server. The safest way to prevent old mail from re-syncing is to keep historical mail in a separate .pst file opened in classic Outlook, instead of importing it into the live synced mailbox.

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  1. Hendrix-V 18,925 Reputation points Microsoft External Staff Moderator
    2026-08-15T02:17:52.6+00:00

    Hi Bernard Gordon,

    This behavior can occur if older Outlook data was imported into a mailbox that syncs with a mail server. For Microsoft 365, Exchange, and Outlook.com accounts, Outlook automatically synchronizes mailbox content between the computer and the server, so imported messages may be uploaded and appear to have been sent back to the source mailbox.

    To help prevent additional synchronization of historical mail:

    1. Check whether the transferred file was a.pst file or an.ost file.
    2. If the old messages are only needed for reference, keep them in a separate Outlook Data File (.pst) rather than importing them into the active mailbox.
    3. If the import has already occurred, review the imported folders and move archive content to a separate local.pst file if appropriate.

    If you can confirm whether the email account is a Microsoft 365/Outlook.com account or a POP account using a local .pst file, the community can provide more specific guidance for your setup.

    I hope this points you in the right direction. Let me know if you need further assistance, feel free to ask me by clicking "Add Comment" or "Add Answer" if you cannot add comment so your response will be visible. Thanks for your effort.

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