How to Extract Email Addresses from OST File

Summary: You can extract email addresses from an OST file in three ways. First, open the OST in Outlook and export contacts or sender lists to CSV. Second, convert the OST to PST and run a PowerShell script to pull To, Cc, From, and Reply-To addresses. Third, use a dedicated OST email address extractor that reads the OST directly and saves unique addresses to CSV or TXT. A companion guide shows how to extract attachments from OST in the same workflow. The dedicated tool is the fastest. The PowerShell route is the most flexible for IT users.

Why You Might Need to Extract Email Addresses from an OST File

OST files store an offline copy of a mailbox from an Exchange, Microsoft 365, or IMAP account. If you only need to read the messages, see how to view an OST file in Outlook first. Over time, those files build a rich list of contacts.

However, OST is tied to the original Outlook profile. As a result, you cannot just open it on a new computer to pull addresses out.

People extract addresses from OST for several reasons. For example, they rebuild a contact list after a job change, run a mail merge, clean up duplicates, or migrate to a new CRM. In each case, you need a clean CSV of unique addresses.

What You Need Before You Start

First, gather the basics. Then pick the method that matches your tools and skill level.

• The OST file (usually in %LOCALAPPDATA%\Microsoft\Outlook).
• Outlook installed on the same machine, if you want Method 1.
• Admin rights to run PowerShell, if you want Method 2.
• A target CSV or TXT location with enough free space.
• A backup copy of the OST in case anything goes wrong.

Method 1: Export Addresses from Outlook (When OST Is Mounted)

This is the easiest route when the OST still loads in Outlook on your PC. You let Outlook do the parsing, then export.

Open the OST in Outlook

First, sign in to the same profile that owns the OST. Then wait for Outlook to sync the folders you need.

If the profile is gone, jump to Method 2 or Method 3. Outlook will not open an OST from a missing profile.

Export contacts or sender lists to CSV

Next, go to File > Open & Export > Import/Export > Export to a file > Comma Separated Values. Then choose the Contacts folder and save a CSV.

For senders inside mail folders, use the People pane or a custom search folder. Finally, copy unique From and To values into a clean CSV.

Method 2: Convert OST to PST and Use PowerShell

IT users often prefer this route. You convert the OST to a portable PST, then run a script that reads every message header.

Convert the OST to PST

First, mount the OST in Outlook and export the mailbox to a PST. Alternatively, use a free OST to PST converter when the profile is missing, or follow our steps to restore an OST file in Outlook first.

Then store the PST on a local drive with at least 2x the OST size as free space.

Run the PowerShell script

Next, open PowerShell and load the Outlook COM object. Then loop through every folder and message, and collect To, Cc, From, and Reply-To values into a HashSet.

Finally, export the HashSet to a CSV. As a result, you get a deduplicated list of every address that ever touched the mailbox.

Method 3: Use a Dedicated OST Email Address Extractor Tool

Sometimes Outlook will not open the OST and PowerShell is overkill. In that case, a dedicated extractor is the fastest path.

When to choose this method

Choose this route when the OST is orphaned, the profile is gone, or you need to process many OST files at once. Additionally, it helps when you want a single CSV with To, Cc, From, and message-body addresses combined.

Steps

First, download the OST email address extractor on your PC. Then install the setup and launch the tool.

Next, click Open on the application screen.

Then choose Email Data File and select the Outlook OST file from your computer.

Next, the tool loads every folder on the left panel. You can preview messages before extraction.

Then click Extract and pick Email Addresses from the drop-down list.

Next, pick the fields you want (To, Cc, From, Message Body, Message Header). For example, choose only From to get a clean sender list.

Finally, browse to the destination folder and click Save. The tool writes a deduplicated CSV with every unique address.

Which Method Should You Choose?

Use Method 1 (Outlook export) when the OST still mounts and you only need the Contacts folder.

Use Method 2 (PowerShell) when you are an IT user who wants control over deduplication, field selection, and scripting. Also use it when you must run the job on a schedule.

Use Method 3 (dedicated tool) when the OST is orphaned, you have many files, or you want a single CSV with every address from headers and bodies.

Frequently Asked Questions

Can I extract email addresses from an OST file without Outlook?

Yes. A dedicated OST extractor reads the file format directly. Therefore, Outlook does not need to be installed.

Will the extracted CSV include duplicates?

No, if you use a dedicated tool or a PowerShell HashSet. Both deduplicate addresses automatically.

Can I pull addresses from only sent items or only received mail?

Yes. Select the folder before running the export, or pick only the From or To field at extraction time.

Is the OST file modified during extraction?

No. Extraction is read-only. The OST stays untouched. However, always keep a backup before any conversion step.

What if my OST is encrypted or password protected?

Mount the OST in the original Outlook profile first. If that is not possible, use a dedicated extractor that supports password-protected OST.

How big an OST can I process?

Most dedicated tools handle OST files of 50 GB or more. The main limit is free disk space for the output CSV.

Related Guides