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Convert PST to EML

EML is the most portable email format: one standard file per message that almost every mail program, archive and e-discovery tool can read. Converting a PST to EML makes old Outlook mail usable anywhere.

Updated 2026-10-26 · 4 min read

In the browser

  1. Open the PST (or OST) in Letterlark.
  2. Pick a folder or search, select the messages.
  3. Choose EML – you get a .zip with one .eml per message, named by date and subject.

The messages are rebuilt as standard RFC 5322 emails with their HTML/text bodies and attachments.

With readpst

readpst -e -o out/ archive.pst writes one file per message with the libpst tools (Linux/macOS). Free; command line only.

What doesn't carry over

  • Outlook-only properties (categories, follow-up flags, read status) are not part of the EML standard.
  • Calendar items, contacts and tasks are not emails; they show as text in the viewer.
  • S/MIME-encrypted messages stay encrypted.

Next step: import the EML files

  • Thunderbird: with the ImportExportTools NG add-on, import a folder of EML files.
  • Apple Mail: drag .eml files into a mailbox, or convert to MBOX instead (PST to MBOX) and use File › Import Mailboxes.

Open your mail file now. Letterlark opens PST, OST, MSG, EML and MBOX files in Chrome, Edge, Firefox or Safari on Windows, Mac, Linux or Chromebook. Files are read on your computer – the app page cannot upload anything. Viewing and search are free without limit; exports (PDF, EML, MBOX, CSV, attachments) are free up to 20 messages at a time. A one-time license is $19 (Personal) or $49 (Pro, business use).

Open Letterlark – free

Questions and answers

EML or MBOX – which should I choose?

EML for archiving or tools that want one file per message; MBOX to import a whole folder into Thunderbird or Apple Mail in one go.

Is the free version enough?

It exports 20 messages at a time, enough to test. For whole folders, a $19 one-time license removes the limit.

Sources and product names: RFC 5322; libpst readpst manual; Thunderbird ImportExportTools NG documentation. Microsoft, Outlook, Gmail, Google Takeout, Apple Mail and Thunderbird are trademarks of their owners. Letterlark is independent and not affiliated with them.