What this fixes
A Microsoft 365 Group does two things with every email sent to it. First, it delivers a copy to every subscribed member, straight into their normal mailbox. Second, it keeps its own copy in the Group mailbox, which is the shared archive everyone can browse.
That second copy is the one that quietly grows. After a few years of newsletters, notifications and attachments, a busy Group mailbox can fill up and start refusing new mail. Clearing out messages older than 12 months frees that space back up.
Deleting old messages from the Group mailbox does not touch copies already delivered to members. Everyone keeps the emails sitting in their own inbox, and members carry on receiving new Group email exactly as before.
Before you start
Choosing “12 months and older” permanently deletes those older Group mailbox copies.
They cannot be restored from the Group mailbox afterwards. If anything in the archive still matters, save or export it first.
- You need to be a member of the Group in Microsoft 365.
- Use Outlook on the web — the Manage storage page isn't in the desktop app.
- Allow about five minutes, plus a few more for storage totals to update.
Step-by-step
Opens https://outlook.office.com/groups/home in a new tab.
Step 1: Open Outlook Groups on the web
Go to the Microsoft 365 Groups page in Outlook on the web. It works in any modern browser.
Step 2: Sign in with a Group member account
Use a Microsoft 365 account that is a member of the Group you're cleaning up. If you can't see the Group, you're probably not a member yet.
Step 3: Select the Group and open Mail / Inbox
Choose Operations (or whichever Group is full) from the list, then open its Mail or Inbox view so you're looking at the Group's stored messages.
Step 4: Open Settings
Select the gear icon in the top-right corner of Outlook to open the Settings panel.
Step 5: Choose Manage storage
In Settings, go to Mail and then Storage — the page is titled Manage storage. It lists each folder and how much space it uses.
Step 6: Under Inbox, open the dropdown next to Empty
On the Inbox row, select the small arrow beside the Empty button. Don't press Empty itself — that targets everything.
Step 7: Choose “12 months and older”
Pick 12 months and older so only messages older than a year are targeted. Anything from the past 12 months stays where it is.
Step 8: Confirm with OK
Outlook shows a warning that these items will be permanently deleted. Read it, then select OK to continue.
Step 9: Wait, refresh, and verify
Give Exchange Online a few minutes to process the cleanup, refresh the Manage storage page, and confirm the used space has dropped and free space increased.
What gets deleted — and what doesn't
What gets deleted
- Group mailbox copies of messages 12 months and older
- Attachments stored inside those old Group messages
- The storage space those items were using
What does not get deleted
- Copies already delivered to members' personal mailboxes
- Group messages from the past 12 months
- Files in the Group's SharePoint site, OneNote or Planner
- Group membership, subscriptions and future email delivery
Troubleshooting
A note for APS
APS staff don't have to run this cleanup themselves. If you'd rather we handle the Group mailbox — including checking retention holds and confirming nothing important is removed — just contact CYBER904 and we'll take care of it.