Convert OST to EML Online

The free online mail converter that transforms EML, MSG, PST, and MBOX files into PDF, HTML, Word, and more — no software required.

CoolUtils online mail converter supports all major email formats as input — EML, MSG, PST, OST, and MBOX — and converts them to PDF, HTML, DOC, TXT, JPEG, and other output formats. Upload the file, select the output format, and download the converted document in seconds. No installation, no registration, completely free.

CONVERT OST to EML ONLINE

1) Upload OST file to convert

Drop files here, or Click to select

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Allowed file types: pst, ost, eml, msg, mime, smime, p7m, mbox, dbx, vcf, vmbx, opf, asice, cpgz, lzh, zcf

2) Set converting OST to EML options

3) Get converted file

DOWNLOAD CONVERTED FILE

Full version

Get Total Outlook Converter to convert your Outlook emails safely.

Total Outlook Converter To Convert Outlook emails

Convert Outlook emails in batch!;
Convert PST to PDF, DOC, TIFF, TXT, HTML, EML and more
Convert hundreds of files in 3 clicks;
Have a desktop converter that works without Internet;
Keep your emails safe, don't send them to the web;
Get more accurate results with the more poweful engine.

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Total Outlook Converter

Convert Outlook emails from multiple sources to a variety of formats.

Filter emails by sender, subject, date, keywords, and more.

Useful data saving options - convert only necessary data from your emails.

Unique output files formatting options specify how your files will look.

Affordable Price - pay once for a lifetime license with no hidden fees.

Command Line Support - convert emails via command line.

Fast batch conversion - convert multiple emails simultaneously.

High security options - protect your output PDF files (if you choose PDF).

Various file naming and date saving options - organize your output files easily.

Variety of attachment saving options - choose how to save attachments.

Trust - you can rely on powerful email converters from CoolUtils.

Easy to use even for beginners - enjoy clear user-friendly interface.

How to convert OST to EML?

💾 Upload Your File: Go to the site, click on «Upload File,» and select your OST file.

✍️ Set Conversion Options: Choose EML as the output format and adjust any additional options if needed.

Convert and Download: Click 👉«Download Converted File»👈 to get your EML file.

Cloud Based

There is no need to install any software to convert OST to EML with CoolUtils. Simply access the internet, and you can easily convert your file online with our service.

Secure

Our hardware operates in top-tier, highly secure data centers equipped with advanced electronic surveillance and multi-factor access control systems.

Ease of Use

Converting OST offline Outlook archives to EML files online has never been so simple. Drop your .ost file and the converter extracts each email as a separate .eml — readable in every mail client without Outlook installed.

Privacy

We understand the importance of privacy, which is why we've developed a comprehensive privacy policy detailing how we handle your files and personal information. You can read the policy here.

OST File

File extension	.OST
Category	File
Description	OST is an offline data file used by Microsoft Outlook to store emails, calendars, and other information when working in cached mode with an Exchange server.
Associated programs	Microsoft Outlook, SysTools OST Viewer, Kernel OST Viewer
Developed by	Microsoft
MIME type	application/vnd.ms-outlook
Useful links	More detailed information on OST files
Conversion type	OST to EML

EML File

File extension	.EML
Category	Document File
Description	EML files are commonly used for email files generated in Outlook Express and other mail systems. EML emails are stored in standard MIME RFC 822 format. These files include the email headline and body in text ASCII format. Emails, attachments, and hyperlinks are all included when converting EML to PDF. Users can export EML files for archiving and storage and check for harmful code. EML files are compatible with Microsoft Entourage, Apple Mail, Thunderbird, IncrediMail, Outlook Express, and more.
Associated programs	CoolUtils Mail Viewer Apple Mail IncrediMail Microsoft Outlook Microsoft Windows Live Mail Mozilla Thunderbird
Developed by	Microsoft
MIME type
Useful links	More detailed information on EML files

2026-01-16

After our Exchange server was decommissioned, I used this to extract emails from orphaned OST files to EML so users could import them into their new webmail accounts.

Rania Mansour

2026-03-28

Recovered a disconnected OST archive from a former employee's machine — converting to EML let us import the emails into our legal hold mailbox without losing any messages.

Pieter van den Berg

2026-05-09

Used this tool to migrate emails from an OST left over after an Office 365 migration; the EML output imported cleanly into Thunderbird for review.

Luciana Moretti

Rating OST to EML

4.7 (390 votes)Rate It

OST to EML Converter — Frequently Asked Questions ▼

What is an OST file?

OST (Offline Storage Table) is the local cache Outlook keeps for an Exchange, Microsoft 365, IMAP, or Outlook.com account. It mirrors the server mailbox so Outlook works offline, and is bound to the original profile — unreadable once that profile is removed.

Why convert OST to EML?

EML is the per-message format almost every mail client opens directly. Splitting an OST into EML rescues cached mail as individual files you can browse in Explorer, migrate to Thunderbird or Apple Mail, attach to tickets, or feed to an e-discovery review platform.

How do I convert OST to EML online?

Upload your .ost file using the button above. The converter parses the offline cache, walks every folder, extracts each cached message, and writes one .eml per email into a ZIP archive ready to download.

Are folder structures preserved?

Yes. The resulting ZIP contains a directory tree mirroring the Outlook folder hierarchy (Inbox, Sent Items, custom folders), each holding the EML files that belong to it.

Are headers, attachments, and inline images preserved in the EML output?

Yes. Each output .eml is a faithful RFC 822 copy of the cached message — From, To, Cc, Subject, Date, the HTML body, inline images, and all attachments. Opening it in Thunderbird, Outlook, Apple Mail, or Windows Mail produces exactly the message as it appeared inside Outlook.

Can I batch-convert many OST files?

Online conversion is one file at a time. For batches, use Total Outlook Converter on your desktop: TotalOutlookConverter.exe C:\ost_files C:\eml_out /ConvertTo eml processes an entire folder in one run.

Are my uploaded files kept private?

Uploaded files are deleted automatically after you download the result. They are not stored, indexed, or shared. For confidential or regulated mailboxes, run the conversion locally with Total Outlook Converter on your own machine.

Convert OST to EML — Extract Cached Outlook Mail as Individual Emails

OST is the offline cache Outlook builds for an Exchange or Microsoft 365 account, tied to that single profile. EML is the per-message email format almost every mail client opens directly. Converting OST to EML extracts each cached email as its own .eml file, ready to browse, attach, migrate to Thunderbird or Apple Mail, or feed to an e-discovery review platform. Drop your .ost file above.

What Is OST?

OST (Offline Storage Table) is the local cache Outlook maintains for an Exchange, Microsoft 365, IMAP, or Outlook.com account. The file lives under your user profile and mirrors the server-side mailbox. OST is encrypted against the original profile — without that profile and that machine, Outlook cannot open it.

What Is EML?

EML is the per-message email format used by Outlook Express, Windows Mail, Windows Live Mail, Thunderbird, and many other clients. Each .eml is plain RFC 822 text — headers, body, MIME-encoded attachments — saved with the .eml extension. One file holds one email. Almost every mail client opens .eml by double-click, and Windows Explorer shows a built-in preview.

OST vs EML — Format Comparison

Property	OST	EML
Purpose	Offline cache of a server mailbox	Single-message email file
Messages per file	Whole mailbox	One
Tied to profile	Yes (encrypted to the profile)	No
Native readers	Outlook with original account	Almost all mail clients
Browse in Explorer	Opaque	Preview pane works
Cross-client portability	None	Universal
Typical use	Local cache	File-per-email storage

When Do You Need OST to EML Conversion?

Rescue mail from an orphaned OST when the original account has been deleted
Migrate cached Outlook mail into Thunderbird, Apple Mail, or another EML-friendly client
Produce EML exhibits from a cached mailbox for e-discovery review
Browse cached mail one message at a time in Windows Explorer
Attach individual cached emails to tickets, cases, or chat threads
Index a cached mailbox in a system that crawls one .eml per item

Command-Line Conversion

Batch-convert an entire folder without opening the interface:

TotalOutlookConverter.exe C:\ost_files C:\eml_out /ConvertTo eml /ProcessRecursively

Add /ProcessRecursively to include subfolders. Save the command in a .bat file for scheduled or automated runs.

Online vs Desktop

Feature	Online (this page)	Total Outlook Converter (desktop)
File size limit	50 MB	Unlimited
Batch conversion	One file at a time	Entire folders at once
Software install	None required	Windows 7–11
Output options	Standard	Full control
Command-line	No	Yes
Privacy	File uploaded to server	Stays on your computer
Price	Free	From $49.90

Convert OST to EML Online