Microsoft 365 / Outlook
Microsoft 365 error 554 5.2.2 — mailbox full (QuotaExceeded)
554 5.2.2
The recipient's Exchange Online mailbox has exceeded its storage quota, so the message was rejected rather than delivered. Unlike Gmail's temporary 452, Exchange commonly returns this as a permanent 5xx — the message will not be retried, and the sender gets an NDR immediately. The fix belongs to the recipient (or their admin); the sender's only real decision is what the bounce means for their list.
How to fix it
- 1
If you're the sender
Nothing on your side caused this and re-sending hits the same wall until the recipient clears space. For anything important, use another channel. On mailing lists, treat repeated 5.2.2s from an address the way you treat a hard bounce: suppress it until it proves alive.
- 2
If you're the recipient
Delete large mail (sort by size, empty Deleted Items and Junk — they count against quota), or archive old mail out of the mailbox. Outlook shows current usage under Settings → General → Storage.
- 3
If you're the recipient's admin
Check the mailbox's quota in the Microsoft 365 admin center or Exchange admin center (ProhibitSendReceiveQuota is the limit that triggers this NDR). Raise it within your license's cap, enable archiving, or clean up — and check whether some rule or connector is ballooning the mailbox, like a journaling loop.
- 4
If it's a shared or resource mailbox
Shared mailboxes without a license have a lower quota cap and hit 5.2.2 sooner than user mailboxes. Assigning a license or enabling archive raises the ceiling.
Meaning current as of 2026-07-25, cross-checked against the provider's own documentation. Providers do occasionally redefine codes — if this doesn't match what you're seeing, the source link is the authoritative reference.