Opening OST Files

The OST file type is primarily associated with Outlook.

OST	File extension: OST
	File type:	offline cache

What is an OST file?

OST files mostly belong to Outlook by Microsoft. An OST file contains a locally saved copy of emails, contacts, tasks, and calendar information synchronized or downloaded for an IMAP, Outlook, or Exchange email account. By saving a local copy of an email account's data as an OST file, Outlook is able to retrieve such information without Internet access. Messages, contacts, appointments and other entries created by a user when Outlook is offline are also saved in an OST file until Outlook is able to establish a connection to the email database. Another type of OST file is a construction and project takeoff estimate created by On-Screen Takeoff.

How to open OST files

You need a suitable software like Outlook to open an OST file. Without proper software you will receive a Windows message "How do you want to open this file?" or "Windows cannot open this file" or a similar Mac/iPhone/Android alert. If you cannot open your OST file correctly, try to right-click or long-press the file. Then click "Open with" and choose an application. You can also display a OST file directly in the browser:. Just drag the file onto this browser window and drop it.

Online OST Text Viewer

Choose your .ost file to analyze

or drag and drop it here

Online File Viewer

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OST file format:

To view or edit OST files you need to know the file format, because it determines how the data in this file is stored. The file format can be determined based on the file extension and the signature (the first few characters of a file). However, different programs can use the same file extension. Furthermore, a file extension can be renamed incorrectly and double-clicking on it will then display an error when it is opened. So you need a detailed analysis of a file to find out the format and the associated program. Below you will find our evaluation of the OST files:

The OST file extension mainly uses a special format. The two most popular formats are as follows:

• 90% of all OST files are Microsoft Personal Folder File files. The contents of these files cannot be read by a human; only a computer program can interpret the data. Most of these files are 16 MB to 330 MB in size. The file type was developed 10 years ago and is still in use today. Certain words are almost always found in the files, such as !BDN. These files can be linked to outlook, gmail, hotmail, mail, mermaid, gloriarosetrinidad, ryanwilsdon, acnoutlook and huser, and usually contain person-related data.
• 2% of all OST files start with the bytes 1A 2C 21 7A D9 FA 7C 48 28 60 A4 30 19 84 A2 3A, which are crucial for this file format. These files are binary files, so they do not contain text, but only cryptic characters. The files are on average 210 MB in size and range from 210 MB to 210 MB. Some examples of file names are J_Mangaccat-yahoo.com(2).ost. Such OST files store data about mangaccat and yahoo.

All other OST files (8%) have no consistent format. You can get all the details of your OST file by dragging it onto this page or by clicking the button "Choose your .ost file to analyze" above.