An IMAP OST is the strangest of the family. Most of what is in it does not need converting at all, because the server already has it - and the small part that genuinely matters is the part people forget until it is gone. This page separates the two before you waste effort, or lose the wrong thing.
With Exchange, the OST mirrors a mailbox. With IMAP, the picture is split: mail lives on the server and the OST is just a local speeding-up of it, while some Outlook data lives only in the OST and exists nowhere else on Earth. Converting an IMAP account without knowing which is which leads to the classic double failure - hours spent exporting mail that would have downloaded by itself, and a calendar silently lost.
IMAP is a server-first protocol. Your Inbox, sent mail and folders live on the mail server; Outlook downloads copies into the OST so reading is fast and works offline. Moving to a new PC or a fresh profile therefore needs no conversion for mail at all - add the account, wait for the sync, and the mailbox rebuilds itself. Exporting IMAP mail to a PST is only worth it as an extra offline archive, or when the account itself is about to be closed.
One limit to know: Outlook may only have downloaded the recent mail into the OST, depending on the sync slider in account settings. Anything older lives on the server only - another reason the export of an IMAP OST can look mysteriously small.
IMAP carries mail and nothing else. So when you create a calendar, contacts or tasks under an IMAP account in Outlook, Outlook stores them in special local folders labelled (This computer only) - inside the OST, and nowhere else. They do not sync to the server, they are not in your webmail, and no new PC will ever download them.
Plan the move around this table and nothing important gets left behind by assumption.
| Item | Travels in a PST | Honest note | ||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| M | a | i | l | a | n | d | f | o | l | d | e | r | s | |||||||||||||||||||||
| Y | e | s | ||||||||||||||||||||||||||||||||
| F | o | r | I | M | A | P | t | h | i | s | d | u | p | l | i | c | a | t | e | s | t | h | e | s | e | r | v | e | r |
On the old PC: export the This computer only calendar and contacts (plus a full-mail archive only if the account is closing). On the new PC: add the IMAP account and let mail resync, then import the small PST for calendar and contacts. Twenty quiet minutes, no converter tools, and - unlike most IMAP horror stories - an ending where the address book survives.
Watch the video for the export wizard in action - the same steps rescue the This computer only folders this page is about.
▶️ Watch Full VideoFor mail, no - it resyncs from the server when you add the account on the new PC. For the calendar and contacts folders marked This computer only, yes, absolutely - export those to a PST first, because they exist nowhere else.
Because a whole-mailbox export starting point can still miss it if the calendar was never selected, or people export only the Inbox out of habit. Re-run the export choosing the Calendar (This computer only) folder itself and it will come across.
No. One is the fresh empty list from the new account setup and one is your imported contacts. Once you confirm the imported list is complete, you can remove the empty one or set the imported list as the default address book.