Outlook keeps a full local copy of every mailbox you have added
The Outlook profile stores every message and attachment locally, and removing an account does not always remove its data. Where it is and how to shrink it.
Outlook is a local copy of your mail, not a window onto the server, and that is the whole explanation for its size. Every message, every attachment and every calendar item in every account you have ever added is written to disk and stays there until something removes it.
Where the profile lives
du -sh ~/Library/Group\ Containers/UBF8T346G9.Office 2>/dev/null
du -sh ~/Library/Group\ Containers/UBF8T346G9.Office/Outlook/* 2>/dev/null | sort -h | tailRecent versions keep everything under a shared Microsoft group container rather than in your Documents folder. Inside it, one folder per profile, and each profile holds the message database and a separate store of attachments.
The three things that make it large
| What | Why it grows | What to do |
|---|---|---|
| Attachments | Downloaded with every message | Set messages to sync a shorter period |
| Removed accounts | The profile is not deleted with the account | Remove the profile in Outlook Profile Manager |
| Old profiles | An upgrade or repair creates a new one | Delete profiles you do not use |
Shrinking it without losing mail
- In Outlook preferences, set how much mail to keep locally. Anything older stays on the server and downloads when opened.
- Empty the Deleted Items and Junk folders in each account, then check the size again.
- Open the Outlook Profile Manager and remove profiles belonging to accounts you no longer use.
- Quit Outlook fully before measuring, or the database rewrites as you look at it.
That last point matters more than it sounds: the database is compacted on quit, so a size measured with the app running is not the size you will end up with.
If you use Apple Mail as well
Both keep their own complete copy, so a Mac with both configured for the same account stores that account twice. Apple Mail's attachments and downloads covers the other half, and it has a separate downloads folder that survives deleting the messages.
Common questions
Where does Outlook store data on a Mac?
In the shared Microsoft group container under ~/Library/Group Containers/UBF8T346G9.Office, with one folder per profile holding the message database and attachments. It is not in Documents on recent versions.
How do I reduce Outlook's storage on a Mac?
Set a shorter sync period in preferences so older mail stays on the server, empty Deleted Items and Junk in each account, and remove profiles for accounts you no longer use. Quit Outlook afterwards so the database compacts.
Does removing an account in Outlook delete its local data?
Not always. The profile can remain with its full copy of the mailbox. The Outlook Profile Manager is where profiles are removed properly, and that is what frees the space.
Why is Outlook larger than my mailbox on the server?
Because it stores attachments alongside the message database and keeps items you deleted until those folders are emptied. A profile left over from a previous account adds a second complete copy.