Mailbox Full? Fix Storage Limits in Microsoft 365 and Google

Mailbox storage limits by plan (Microsoft 365 and Google)

First find out which limit you hit. The figures below come from Microsoft's Exchange Online limits and Google's Workspace storage FAQ for admins, checked in October 2026.

Microsoft sends a warning at 98 GB, blocks sending at 99 GB and rejects incoming mail at 100 GB, returning a non-delivery report to the sender. On Google Workspace, an organisation that goes over its pool keeps email working, but a user who goes over a limit set by the admin loses the ability to send and receive Gmail, according to Google's article on setting user storage limits.

Quick fix today: free up space in Outlook

If the mailbox has already stopped sending, these steps usually clear enough space within an hour. Large attachments are almost always the cause, not the number of messages.

1. 1

   Sort or search by size

   In Outlook, sort the message list by Size (or use the search filters for large items), then delete or save the attachments you no longer need in the mailbox.

2. 2

   Save big attachments to OneDrive or SharePoint

   Drag important files into a OneDrive or SharePoint folder first, then delete the email or remove the attachment.

3. 3

   Empty Deleted Items and Junk Email

   Both count toward the 100 GB. Emptied items move to Recoverable Items, which has its own quota and does not count toward the main mailbox limit.

4. 4

   Clean Sent Items

   Sent Items often holds years of quotes, drawings and photos. Delete old sent mail with large attachments.

5. 5

   Check the size again

   In Outlook on the web, open Settings > General > Storage to see the mailbox size and which folders use the most space. It can take a while to update.

Before deleting in bulk, make sure nobody needs that mail later. Our guide to recovering deleted emails explains how long Microsoft and Google keep deleted items.

Long-term fix: turn on the Microsoft 365 archive mailbox

The archive mailbox is extra storage that sits alongside the main mailbox. Older mail moves there automatically, and the user still sees it in Outlook under In-Place Archive or Archive.

• Enable it: an admin with the Mail Recipients role turns it on in the Exchange admin centre under Recipients > Mailboxes, as described in Microsoft's enable archive mailboxes article.
• Size: on Business Basic and Standard the archive is 50 GB. On Business Premium, the archive starts at 100 GB and can auto-expand up to 1.5 TB once auto-expanding archiving is enabled, according to Microsoft's archive mailboxes overview.
• Move mail automatically: the default Exchange retention policy moves items to the archive after a set time. You can add a shorter archive tag, for example one year, if mailboxes fill fast.
• Outlook offline file: classic Outlook keeps a local copy (an OST file). Archived mail usually stays online, which also keeps laptops lighter.

Google Workspace storage full: what to check

Because Gmail, Drive and Photos share one allowance, the fix may sit in Drive rather than in email.

• Empty Trash and Spam in Gmail. Both count against storage until permanently cleared, says Google's storage help.
• Search Gmail for large messages: type larger:10M or has:attachment larger:5M in the search box, then delete what you do not need.
• Check Drive: sort Drive by storage used and remove large videos, duplicates and old exports. Shared drives count toward the pool too.
• Check the admin side: in the Admin console under Storage, see the organisation total, the heaviest users and any user storage limit you set.
• Know the organisation rule: if the organisation goes over its pool by 25% or for 14 days, whichever comes first, Drive and Docs stop accepting new files, though Gmail keeps working.

Storage counts can lag. Google says the Admin console page can take up to 24 hours to update after a clean-up.

Upgrade or clean up? Doing the maths

Cleaning a mailbox takes staff time every few months. Upgrading costs money every month. Compare them honestly.

Sources: Microsoft 365 business plans for Singapore and Google Workspace pricing. For one heavy user on Google Starter, moving the whole company to Standard can be expensive, because Google applies the same edition to everyone. For Microsoft, licences can be mixed per user. Our guides on Google Workspace Starter vs Standard and whether Business Premium is worth it go deeper.

Shared mailboxes and leavers filling up

Shared mailboxes such as accounts@ or sales@ grow fast and are often forgotten. Without a licence they are capped at 50 GB. Microsoft's limits page says an Exchange Online Plan 2 licence raises a shared mailbox to 100 GB. Archiving can also be turned on for shared mailboxes.

Leavers' mailboxes converted to shared mailboxes are a common source of large, unlicensed mailboxes. Decide how long you keep them, and back them up before deleting anything.

Do it yourself or get help?

A single full mailbox is usually a 30-minute job with the steps above. Get help when several mailboxes are full, the archive is not appearing in Outlook, or you are not sure which retention settings are safe to change.

Our Quick Fix (1 hour) (S$119) clears a full mailbox and turns on archiving. If your email set-up needs a broader rethink, Business Email Setup (S$249) configures Microsoft 365 or Google Workspace properly on your own domain.