Archive old emails in Outlook

First: the Archive button does not free space

In Outlook, Outlook on the web and on phones, the Archive button moves a message into a folder called Archive. That folder is still inside your mailbox, so it still counts against your storage. It tidies the inbox; it does not shrink anything.

To free space you have to move mail out of the mailbox: into a PST file on your computer, or into an online archive if your organisation provides one.

See what takes the space

In classic Outlook for Windows: File › Info › Tools › Mailbox Cleanup › View Mailbox Size. It lists every folder with its size. Usually a few folders (Inbox, Sent Items, a project folder with attachments) hold most of it.

Quick wins before archiving:

• Empty Deleted Items and Junk Email.
• Sort a large folder by Size and deal with the biggest messages first.

Move old mail into a PST (classic Outlook for Windows)

1. File › Info › Tools › Clean Up Old Items (called Archive in some versions).
2. Choose Archive this folder and all subfolders and select the mailbox or a folder.
3. Set Archive items older than, for example one or two years ago.
4. Check where the Archive file will be saved (by default archive.pst in Documents\Outlook Files) and click OK.

Outlook moves the old items into the PST and shows it in the folder list as Archives. The mailbox shrinks once the server catches up.

Automatically: File › Options › Advanced › AutoArchive Settings runs the same thing on a schedule.

If Clean Up Old Items or AutoArchive is missing, your organisation probably manages archiving through an online archive (a second mailbox on the server) or retention policies. Ask your IT team before creating PSTs: some organisations do not allow them.

New Outlook for Windows and Outlook on the web cannot create PST archives. See PST files in new Outlook.

Keep the archive itself healthy

An archive that grows for years becomes the next problem: a 30 GB archive.pst is slow to open and search, and if it gets damaged everything in it is at risk.

• Split it by year. Split PST turns one big archive into one PST per year, each holding that year’s mail with its folders. Small files open fast and are easy to back up. Preview the parts for free first.
• Back it up. A PST on your computer is the only copy of what it holds. Copy it to a backup drive or cloud storage you trust, with Outlook closed.
• Check old archives. If an archive will not open, run the free health check in Repair PST before anything else.
• Remove duplicates that pile up from repeated archiving or imports: Remove duplicates.

Size limits to know

Outlook slows down long before these limits. More in PST file too large.

Frequently asked

Can I read an archive PST without Outlook? Yes, in the PST Viewer, in your browser, without uploading it.

Will archiving delete mail? Moving to a PST does not delete anything; the items move to the archive file. Check the AutoArchive setting Permanently delete old items is off if you want to keep everything.