Convert an .olm archive to EML files
EML is one message per file, in the same plain format a mail server sends: headers at the top, body below, attachments encoded inside. It is what you want when you need to hand over twelve specific messages, file mail alongside a project's documents, or feed the archive into something that reads mail files. Double-clicking an .eml opens it in Mail on a Mac and in Outlook on Windows, with no conversion at all.
The file you get
A .zip with one .eml per message, in folders mirroring the Outlook tree. Files are named 2023-05-16 1954 - Pat Levine - Quarterly figures.eml, so a folder of them sorts by date and reads as a list of subjects.
Steps
- Get the .olm out of Outlook for Mac first: Tools tab → Export, tick what you want, Continue, save the file. If Export is greyed out you are in the new Outlook; switch the New Outlook toggle off, top right, and it comes back.
- Drop the
.olmon this page. It is read by JavaScript in your browser tab; the file never leaves your machine. - Choose the folders, or a date range, if you only need part of the archive.
- Download the zip and unzip it. Double-click any
.emlto read it, or drag the files into a mail client, a case folder or a document management system.
What carries over
- One file per message, with the full header block: From, To, Cc, Subject, Date, Message-ID where present
- HTML body plus a plain-text alternative
- Attachments encoded inside the file, so a single
.emlis self-contained - The folder tree as directories, so Sent Items stays separate from Inbox
- File names carrying date, sender and subject, punctuation stripped where a file system would refuse it
Good to know
- Outlook writes times in UTC but leaves the time zone off the timestamp. Every date here is read as UTC, so nothing shifts by your offset, a common fault in other converters.
- Long subjects are truncated in the file name at 80 characters; the full subject is in the file's Subject header.
- Two messages that share a date, sender and subject get
(2)appended rather than overwriting each other. - Archives over about 2 GB are written straight to disk in Chrome and Edge. Safari and Firefox assemble the download in memory, so on a very large archive use Chrome, or convert one folder at a time.
- Microsoft has never published the
.olmformat. Mail, attachments, contacts and calendar entries are read from the XML Outlook writes; unusual items (notes, tasks, journal entries) are skipped in this version.
Questions
What opens an .eml file?
Mail on macOS and Outlook on Windows open one on a double-click. Thunderbird opens them from File → Open → Saved Message. Windows also opens .eml in its built-in Mail app if Outlook is not installed.
Are attachments separate files?
No, they are encoded inside each .eml, which is the point of the format, one file is the whole message. Open the message and save the attachment from there, or use the searchable HTML archive if you want the attachments as loose files.
I need these in Outlook for Windows. Does that work?
Yes, and it is how you end up with a .pst. Make a new folder in Outlook and drag the .eml files into that folder rather than onto the Inbox. The route, including the export that creates the .pst, is on the OLM to PST page.
Can I export only one Outlook folder?
Yes. Untick everything else after the archive loads; only the ticked folders are written.