Understanding Your Mailbox and OneDrive Storage Limits

Both your mailbox and your OneDrive have a storage limit as part of your Microsoft 365 licence. It’s generous for typical day-to-day use, but it’s worth knowing what happens as you approach it.

What happens as you get close to the limit

You’ll usually get an automatic warning email once you’re close to full (typically around 90%). At this point, everything still works normally — it’s just a heads-up to clear some space before it becomes a problem.

What happens if you actually hit the limit

Mailbox full: you’ll stop being able to send or receive new email until space is freed up — incoming mail to you will bounce back to the sender rather than being held for later.

OneDrive full: you’ll stop being able to upload or sync new files, though existing files remain accessible.

Caution

A full mailbox bouncing incoming email is the more disruptive of the two — people emailing you get an error rather than your email simply being delayed, so it’s worth acting on the warning email rather than waiting until it’s actually full.

Freeing up space in your mailbox

• Empty your Deleted Items and Junk folders — deleted emails still count against your limit until these are cleared.
• Find your largest emails (in Outlook, sort your inbox by size) — a handful of emails with large attachments are often most of the problem.
• Move old attachments to OneDrive instead of keeping them in email, and delete the original email once saved.

Freeing up space in OneDrive

• Delete or archive files you no longer need, especially large ones — check your largest files first for the biggest impact.
• Empty your OneDrive recycle bin — deleted files still count against your limit until this is emptied too.
• Avoid keeping large personal files (photos, videos) in your work OneDrive — see Working Safely From a Personal Device for the general principle here.

If you genuinely need more space

If you’re consistently near the limit despite clearing things out, that’s usually a sign your licence tier needs reviewing rather than something to keep managing manually — contact support to discuss options.