Your old mail lives in PST files - years of it. Before switching apps, this one question decides everything: can the new Outlook actually open, search and use those files the way classic does today?
For Indian offices especially, the PST file is the archive of record - old invoices, client threads and years of history sit in local files, not in a cloud mailbox. Classic Outlook opens, imports, exports and repairs these files as a core feature. The new Outlook treats PST as a staged feature: support has been arriving in phases, starting with limited opening and viewing, with fuller abilities promised later. This page states plainly what that means today, so nobody discovers a locked archive after switching.
Example status panel - PST abilities in the new app change by update, so recheck after major updates.
When Microsoft says a feature is coming in stages, it means early builds can do less than the final plan. For PST that has meant first the ability to open a file and look at mail folders, while actions like moving items freely, full search inside the file, calendar and contacts in PST, and importing into the account arrive later or remain limited. The practical result: an archive you could browse in classic may open as a partial, read mostly view in the new app. That is fine for checking one old mail. It is not a working archive system for a desk that lives in old files daily.
Your live mailbox is unaffected by the PST question. Mail stored in your Microsoft 365, Exchange or IMAP account syncs to any app, because it lives on the server. The PST problem only touches mail that exists only in local files - which, in older offices, is often the most valuable mail of all. Also note the new app creates no PST backups: the classic habit of exporting a mailbox to a PST before a PC change has no equivalent button there today, so backup routines built on PST exports belong to classic until that changes.
The pattern that protects everyone is boring and effective. Keep classic Outlook installed on the archive desk. Keep opening and maintaining PSTs there exactly as today, with the usual discipline - one PST per year, stored locally, backed up by file copy. Use the new app, if you like it, only for the live mailbox on other desks. And watch the staged rollout: when full PST support is officially complete in the new app, test it on a copy of an archive file, never on the only copy, before trusting it with the real one.
One genuine exit from the PST world exists: import the archive into the server mailbox using classic Outlook's Import and Export wizard, so the old mail becomes server mail that every app can see. It works, but respect the costs. Mailbox quotas apply - a 50 GB archive needs a mailbox that can hold it. Upload takes time on slow links. And once imported, your archive's safety is the provider's backup policy, not your file copy. Many offices import only the last two or three years and keep older PSTs in classic, which is a sensible split rather than a compromise.
If PST files are your office memory, classic Outlook is your app today - not from nostalgia, but because it is the only one of the two that fully reads, writes, imports, exports and repairs them. The new app's PST story is improving in stages and deserves a fresh test after major updates. Until a test on a copied archive passes every action your desk performs, switching the archive desk is a risk taken with the company's history, and that is never a fair trade for a cleaner interface.
See both Outlook apps side by side in the full video - every difference shown on a real PC, step by step.
Watch Full VideoSupport is arriving in stages and recent builds can open PST files with limited abilities compared to classic. Full import, export and management remain classic Outlook strengths - test your build before relying on it.
No. PST files are local files. They do not sync. Only mail stored in your server mailbox appears automatically in both apps.
Keep them on classic Outlook with your normal backup discipline, or import selected years into the server mailbox using classic. Either way, keep a file copy backup of every archive.