Where Outlook for Mac stores its data

Outlook for Mac keeps mail in a profile folder inside your hidden user Library, under Group Containers. Microsoft describes the application as a locally cached client, meaning the profile is a working copy rather than the master. The newer Outlook for Mac does not use that folder at all.

People go looking for this folder for three reasons. A Mac is being replaced. Something has broken and support has asked for the profile. Or the folder has grown enormous and nobody can explain why. All three end in the same place, so here it is first.

~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/Main Profile

Library is hidden by default, so that path has to be pasted rather than browsed to. A tour of the Library folder explains why Group Containers exists at all. In Finder, open the Go menu, choose Go to Folder and paste it in. Holding Option while the Go menu is open reveals Library for that session instead.

To stop macOS hiding it altogether, one Terminal command does it permanently.

chflags nohidden ~/Library

The Outlook for Mac data location for every version

Microsoft publishes two locations, one for the current generation and one for the version that came before it. Its guidance groups both with Microsoft Entourage, the application Outlook replaced on the Mac, as purely locally cached clients.

Two details in that table catch people out. The folder is called Outlook 15 Profiles on every version from 2016 onward, so the number tells you nothing about which Outlook you run. And the 2011 path sits in Documents rather than Library. Anyone who upgraded from that era looks in the wrong place for years.

Inside Outlook 15 Profiles sits a folder per profile. Unless somebody deliberately made a second one, there is exactly one and it is called Main Profile.

What is inside the Outlook for Mac Main Profile folder

Open it and the structure is simpler than its reputation.

• FolderMain ProfileEverything one profile holds
• FolderDataThe working store, plus the database files that index it
• FolderMessagesThe individual mail records themselves
• Item.olk15 recordsOne per message, contact, event or task
• DbSQLite databaseIndexes the records and holds the structure around them

That split is the single most useful thing to understand about this folder. An .olk15 item carries content without context. Which folder it belonged to, whether it was read and how it threads all live in the database beside it, not in the item.

This is why copying the message files alone never works. People pull the .olk15 items out, move them to a new Mac and get an empty Outlook. The records arrived. The thing that knew what they were did not.

Where the new Outlook for Mac keeps its cache

The newer client is a different application rather than an update to the old one. It ignores the profile folder entirely and keeps what it needs inside its own sandboxed container.

~/Library/Containers/com.microsoft.Outlook/Data

A temporary store inside that container can grow to gigabytes across thousands of hex named folders. Some of what sits there is mail the user already deleted.

No version of Outlook for Mac has ever used a PST or an OST. Several pages claim the Mac data file is one or the other. It is not. It never was. Both belong to Outlook for Windows, so looking for one on a Mac is a search that cannot succeed.

Microsoft's guidance on that temporary store is to leave it alone while Outlook is running. To accept that clearing it can affect undo and recovery for recently handled mail. It refills on its own.

Why the answer depends on your account type, not your Outlook version

Which Outlook you run tells you where to look. How the account was set up tells you whether anything there is worth protecting. That is the more useful question of the two.

Read more: What IMAP and POP actually store on your Mac.

So the honest answer to where Outlook for Mac stores your email is that it depends on how the account was set up. On a Microsoft 365 or IMAP account the profile is a convenience. On a POP account it is the mailbox. Treating it as disposable is how people lose fifteen years of mail during a Mac migration.

Where On My Computer folders are stored

This question arrives on its own, nearly always from somebody about to uninstall or reinstall Outlook who wants to know what they stand to lose.

On My Computer folders are not a separate file kept somewhere else. They sit in the same profile, in the same store, alongside the mail that came down from the server. Nothing distinguishes them on disk.

What distinguishes them is that no copy exists anywhere but that folder. Server mail comes back on its own after a reinstall. On My Computer folders come back only if you kept them.

Before you reinstall Outlook, look at what that section holds. Empty means a reinstall costs you nothing, because the server refills everything. Anything at all in there means the profile is the only copy and a reinstall without a backup destroys it.

What you can and cannot do with the Outlook profile folder

Microsoft is unusually direct about the limits here. They are worth reading before you move anything.

Why the no relocation rule exists. The client keeps its cache on local storage it controls. A network volume that drops or an external disk that sleeps, leaves a half written database behind. That is a corrupted profile rather than a slow one.

On a server backed account there is nothing to recover and Outlook on the web reaches the same mailbox from any browser while you rebuild. If you have already deleted a profile and the account was POP, stop using the Mac for anything else and check Apple's Time Machine first. The user Library is included in a default backup, so a snapshot from before the deletion holds the folder intact. Restoring it into the same location gives Outlook back what it had.

What to back up from Outlook for Mac if you want the mail itself

Copying the profile gives you a profile. That is the right answer if you are moving between Macs and staying in Outlook. It is the wrong answer for almost everything else.

If the goal is mail you can still read in five years, without needing this particular application to read it, the profile is not the thing to keep. An export produces an OLM archive, which is portable in a way the working store is not. An archive exported from the application is portable in a way the working store is not. Converting that archive puts the contents into formats anything can open. The reason this matters more than it used to is the October 2026 change to legacy Outlook for Mac.

Two rules cover most situations. Copy the whole profile when you are moving to another Mac this week. Export and convert when you want the mail to outlive the application. The second route turns a folder only Outlook understands into files anything can open. An OLM converter for Mac does that step.

Whichever you choose, quit Outlook before you copy anything. Then check what you got rather than trusting a folder size.