AutoArchive is the classic Outlook feature that moves old emails, calendar items and tasks out of your mailbox into a separate archive file on your PC. It is still useful when your mailbox is close to full, but it works differently from what many guides describe, and on Microsoft 365 there is often a better option. Here is how to set it up, and when not to.
Quick answer
In classic Outlook, go to File > Options > Advanced > AutoArchive Settings, tick Run AutoArchive every, choose how old items must be, and pick where the archive .pst file goes. On a Microsoft 365 work mailbox, ask IT about the Online Archive instead; it keeps old mail on the server, searchable from any device. The new Outlook for Windows has no AutoArchive.
AutoArchive, Archive button, Online Archive: which is which
| Feature | What it does | Where the mail goes |
|---|---|---|
| AutoArchive (classic Outlook) | Moves items older than a set age on a schedule | A .pst file on your PC |
| Archive button / Backspace | Moves selected emails out of the inbox | The Archive folder in your mailbox (still uses mailbox space) |
| Online Archive (Microsoft 365) | Moves old items by retention policy | A separate archive mailbox on the server |
The Archive button does not free any mailbox space; it only tidies your inbox. AutoArchive and Online Archive do.
How to set up AutoArchive in classic Outlook
- Open File > Options > Advanced and click AutoArchive Settings.
- Tick Run AutoArchive every and choose a frequency, for example 14 days.
- Set Clean out items older than, for example 12 months.
- Choose Move old items to and note the path of the .pst file. Avoid the Permanently delete old items option unless you really mean it.
- Click Apply these settings to all folders now, then OK.
For per-folder rules, right-click a folder, choose Properties > AutoArchive, and set a different age or turn it off for that folder (useful for Contacts or a project folder you always need).
If AutoArchive Settings is greyed out or missing, your organization has disabled it by policy. That is common on Microsoft 365 tenants that use Online Archive.
Why PST archives can be a problem
- The .pst file lives on one PC. Lose or reset the PC and the archive goes with it, unless you back it up.
- It is not visible on your phone or in Outlook on the web.
- Large .pst files (over 20 to 50 GB) get slow and can corrupt. Repair them with
SCANPST.EXE, which is in the Office installation folder. - Many companies block PST files for compliance reasons.
For a work mailbox, the Online Archive avoids all of this. I explain how it works in Microsoft 365 online archives.
Opening your archive later
The archive appears as Archives in the folder pane. If it is missing, go to File > Open & Export > Open Outlook Data File and select the .pst. To search it, click in the search box and change the scope to All Outlook Items.
Outlook acting up after archiving? See Outlook disconnected fixes.
Frequently asked questions
Where is AutoArchive in Outlook?
In classic Outlook, under File, Options, Advanced, AutoArchive Settings. The new Outlook for Windows and Outlook on the web do not have AutoArchive.
Does AutoArchive free up mailbox space?
Yes. It moves old items out of your mailbox into a .pst file on your PC, which reduces the size of the mailbox on the server.
Why is AutoArchive greyed out?
Your organization has disabled it with a policy, usually because it uses Microsoft 365 Online Archive or does not allow PST files. Ask your IT team.
Where is the Outlook archive file saved?
By default in Documents\Outlook Files or in AppData\Local\Microsoft\Outlook, named archive.pst. The exact path is shown in the AutoArchive Settings window.
Is Online Archive better than AutoArchive?
For Microsoft 365 work mailboxes, usually yes. Online Archive keeps old mail on the server, available from any device and included in backups and compliance, without local PST files.