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OST to EML Converter

Convert Outlook OST files to standard EML files that open in Thunderbird, Apple Mail and Outlook.

Your files never leave your device

How to convert OST to EML

  1. 1

    Choose your OST file

    Click the upload area or drag files onto it. Nothing is uploaded — files are opened locally.

  2. 2

    Start the conversion

    Press the convert button. Your browser converts the files in seconds.

  3. 3

    Download the result

    Save each file individually or everything at once as a ZIP.

Split Outlook OST files into individual EML files — one per message, named by folder and subject — so you can open, forward or import single emails. Download them all at once as a ZIP.

Read the full guide with screenshots

What is OST?

OST is Outlook’s offline copy of an Exchange or Microsoft 365 mailbox. It has the same structure as a PST but is normally tied to one account — converting it rescues mail from old or orphaned profiles.

What is EML?

EML is the standard single-email file (RFC 822/MIME) saved by Thunderbird, Apple Mail, Windows Mail and most webmail “download message” buttons. It holds the headers, body and attachments.

Is it private?

Yes. Unlike upload-based converters, ZapMorph processes files inside your browser tab, so the file stays on your device. It is never transmitted, stored or logged — close the tab and it’s gone.

Frequently asked questions

Is the ost to eml converter free?

Yes. Convert 1 file a day without an account, or 5 files a day with a free account. Pro removes all daily limits.

Are my files uploaded to a server?

No. The conversion runs entirely in your browser, so your files never leave your device. We only count how many files you convert — never their names or contents.

What is the maximum file size?

Up to 25 MB per file without an account, 50 MB with a free account, and 1 GB on Pro. Very large files also depend on your device’s memory.

Can I convert multiple OST files at once?

OST to EML Converter works on one file at a time and can produce many output files, which you can download together as a ZIP.

Does it work on Mac, Windows, iPhone and Android?

Yes. It works in any modern browser — Chrome, Edge, Firefox and Safari — on desktop and mobile, with nothing to install.

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