Turn an .olm archive into a searchable HTML file
An .olm sitting on a disk is a dead file: it needs Outlook for Mac, and legacy Outlook for Mac loses support in October 2026. An HTML archive is the opposite, one file, opens in any browser on any operating system, with a search box across every message. This is the version to keep for the long term, and the one to hand to somebody who will never install a mail client.
The file you get
A .zip containing archive.html and an attachments/ folder. The HTML file lists every folder and message, shows a message when you click it, and filters the list as you type in the search box. Attachments are linked from the message they came with.
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. - Download the zip and unzip it, keeping
archive.htmland theattachments/folder together. - Double-click
archive.html. Use the search box for a name, an address, a subject or a phrase; click any result to read the message.
What carries over
- Every message: folder, date, From, To, Cc, subject, body
- Attachments as real files in
attachments/, linked from their message - Inline images shown in the message body
- The Outlook folder tree as a sidebar you can click through
- A search box that runs offline, over the full text of every message
Good to know
- Keep the folder together.
archive.htmllinks toattachments/by relative path; moving one without the other breaks the links. - The whole index lives in the HTML file. Above roughly 50,000 messages it is slow to open; split the export by folder or by year in that case.
- 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.
- 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
Does the search work without an internet connection?
Yes. Everything is in the file: no scripts are loaded from anywhere, no requests are made. It works on a machine that has never been online.
Can I put this on a network share for colleagues?
Yes. Copy the unzipped folder anywhere; anyone who can open a browser can read it. There is nothing to install and no licence.
How does this compare with the PDF export?
PDF is for a fixed record copy you print or attach to a file. The HTML archive is for keeping and searching, it holds attachments as files and finds things in a second.
Will it still open in ten years?
It is plain HTML with no external dependencies, which is about as safe a bet as file formats offer. Keep the original .olm next to it anyway.