Outlook PST/OST Corruption
Outlook reporting a corrupted data file sounds like one problem, but it's actually two very different ones wearing the same error message — and which one it is changes whether this is urgent at all.
What's actually happening
Outlook stores mail locally in one of two container file formats, and they play very different roles. A PST is often the only copy that exists — the default for POP3-configured accounts, and for any manually created archive file, since neither of those has a live mailbox on a server backing them up. An OST, by contrast, is a local cache of a mailbox that actually lives on an Exchange, Microsoft 365, or IMAP server; it exists purely for offline access and speed, not as the authoritative copy of anything.
How recoverable this really is
When the damaged file is an OST and the underlying account is still reachable, this is close to a non-event: deleting the damaged OST and letting Outlook reconnect rebuilds it automatically from the server, with the only real cost being the time the resync takes. A corrupted PST is a genuinely different situation, since for many accounts it's the sole copy in existence — a badly damaged one can lose folders, individual messages, or attachments outright, depending on exactly where within the file's internal structure the corruption falls.
The general approach
The first step is establishing which file type is actually involved — Outlook's Account Settings shows this per account, usually next to the account's data file path. For a genuinely irreplaceable PST, Microsoft's own ScanPST.exe repair utility (installed alongside Outlook) is the standard first move, run against a copy of the file rather than the original.
Always run a repair tool against a copy of the PST file, never the original. If an automatic repair goes wrong on a badly damaged file — which does happen — having the untouched original still available means there's still something to try a different approach against.
The "damaged bookkeeping, not necessarily damaged data" logic here mirrors File System Corruption at the application-file level instead of the drive level. See the full directory of recovery software by vendor for options if ScanPST.exe alone doesn't resolve a badly damaged PST.
This page describes the general situation, not a guaranteed fix for your specific case. If you'd rather have someone experienced take a look before you try anything, see what a hands-on evaluation looks like.