What is a .OST file?
OST is an offline cache of a Microsoft Outlook mailbox.
- Did you know
- An OST keeps a local copy of your mailbox so Outlook works without a connection.
- OST stands for Offline Storage Table, the offline twin of Outlook’s PST mailbox file.
- Modern Unicode OST files default to a 50 GB ceiling, up from the legacy ANSI format’s 2 GB limit.
- What Analyser reads
- Open personal-information files: iCalendar .ics/.ical and .vcs (events, times, recurrence, organiser/attendees), vCard .vcf contacts (fields + inline base64 photo), LDIF directory exports and Windows .contact - with Outlook .msg/.pst, IBM Notes .nsf, Exchange .edb and Outlook Express .dbx identified. Email messages (.eml/.emlx/.mbox) now open in a full viewer - see Email above.
- Depth of analysis
- .OST is an identification-grade format: Analyser recognises it from its bytes and decodes the header metadata it carries, rather than opening it in a full viewer. Formats that do get a full viewer are marked "Full" on the formats page.
- Open a .OST file
- Drag a .OST file onto the Analyser home page (or tap to pick one). It is identified entirely in your browser - nothing is uploaded, there is no account, and it works offline once installed.