552 5.2.2 Mailbox Full / Quota Exceeded

What’s actually happening

Your message bounces with a 552 5.2.2 NDR stating the recipient is over quota or has exceeded storage allocation. The 5.x.x class means the server is treating this as permanent — it will not retry on its own. Often only one specific recipient bounces while everyone else on the same send goes through fine. Repeated 552 bounces to the same address over days usually mean an abandoned or unmonitored mailbox.

Common causes

• The recipient's mailbox has hit its hard storage limit and the server refuses new mail outright (permanent 5.2.2) rather than deferring it.
• The recipient account is dormant or abandoned — nobody is clearing space, so it stays full indefinitely.
• Your message is large (big attachments or inline images) and pushes an already near-full mailbox past the limit.
• The recipient's provider sets a low per-mailbox quota, and ordinary traffic fills it.
• You are treating a permanent 5.2.2 like the temporary 452 4.2.2 soft bounce and retrying, which just generates more permanent bounces.

How to fix it

1. Confirm it is the 5.x.x permanent form, not 4.x.xRead the code precisely. 552 5.2.2 is a hard bounce — stop automatic retries, because the receiving server already gave up. 452 4.2.2 'over quota' is a soft bounce that your MTA should keep retrying for the normal queue lifetime. Acting on the wrong class is the most common mistake here.
2. Tell the recipient through another channelSince the message will not reach them by email, contact the person by phone, chat, or an alternate address and ask them to delete mail or empty Trash/Junk to free space. Nothing you change on the sending side fixes a full mailbox you do not control.
3. Shrink the message and resendIf the mailbox is only marginally over, a smaller message may slip in. Move large attachments to a shared link instead of attaching files, strip heavy inline images, and resend once they have cleared some room.
4. Suppress the address after repeated hard bouncesFor bulk or transactional sending, add the address to your suppression list after consistent 552 5.2.2 results. Continuing to hit a permanently full mailbox wastes reputation and inflates your bounce rate.
5. If it is your own mailbox, raise the quotaWhen you administer the recipient (e.g. an Exchange or Google Workspace mailbox you manage), increase the storage quota or archive old mail. In Exchange this is the mailbox's ProhibitSendReceiveQuota; in Workspace it is the user's storage allocation.