OST to CSV — read an offline Outlook file as a table
Open an .ost file without Outlook and export the messages as a CSV table. The file stays on your computer.
About this conversion
An .ost is the offline copy Outlook keeps on disk, and it is usually all that remains once the account behind it is gone. Turned into a table it answers the questions people actually have about such a file: how many messages are in there, from whom, over which years, and which of them carry attachments — before deciding what is worth pulling out.
What the table looks like
One row per message, with these columns — it opens in Excel, LibreOffice, Numbers or Google Sheets:
date,from,to,cc,subject,size,attachments,attachment_names,labels,preview,text 2019-03-14T09:12:00.000Z,Anna Rees <anna.rees@example.com>,Sales team <sales@example.com>,,Q1 figures,48213,1,q1-figures.xlsx,Inbox,Here are the numbers for the first quarter…,Here are the numbers for the first quarter. … 2019-03-15T16:40:12.000Z,Tom Price <tom.price@example.com>,Anna Rees <anna.rees@example.com>,,Re: Q1 figures,9120,0,,Sent Items,Thanks — one question about March…,Thanks — one question about March. …
When an .ost is all that is left
Outlook keeps an .ost for every Exchange, Microsoft 365 or IMAP account it syncs, and opens it only together with that account. Once the account is closed — someone left the company, the mailbox was deleted, the licence ran out — the file still holds the mail, but Outlook will not show it. Here it is read without the account.
What the table tells you
Sort by date to see which years the file covers, by from to see who wrote most. The labels column holds the Outlook folder, so Inbox, Sent Items and archive folders stay apart. Filter attachments above zero to find the messages worth saving with their files — then export just those as .eml or .pst.
Just want to look inside it?
The same tool without converting anything: open a .ost file and read it.
You are not locked into CSV
The file is parsed once and stays open, so the format is picked at the end rather than the beginning: the same .ost can leave here as XLSX, ZIP, EML, MBOX, PDF, HTML, TXT, JSON or PST. Before that you can search it by subject or address, filter by year, sender and attachment type, mark the duplicates and look through the archive overview.
Questions
- Do I need the original account?
- No. The messages are read out of the file itself.
- Which versions are supported?
- Files from Outlook 2003 onwards, including the newer 4 KB format used since Outlook 2013.
- Is the full text of each message in the table?
- Yes, in the last column, on one line per message so the table stays aligned in every spreadsheet program.