Hi @PhilRW
the email data in the single file only goes back one year, but I have several years of data previous to that, which I would like to access.
Cached Exchange Mode is the default when you add an Exchange or Microsoft 365 account. Usually, Outlook configures Exchange and Microsoft 365 accounts to only synchronize 12 months of your email under Cached Exchange Mode.
If you want to sync all emails, move the sync slider to ALL, you can refer to this link:
Control how much mail is kept offline.
Can I merge these three .pst files into the single new Outlook Data File?
In order to prevent damage to data files, it is recommended that you use hardware storage or upload files to OneDrive, and import them to Outlook365.
Import Outlook items from a .pst file in Outlook for PC
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