Apple Mail (iCloud): mailbox full (user is overquota).

The recipient’s iCloud mailbox is full and cannot accept new mail.

How to fix user is overquota.

Retrying or final
Check the reply
This string has no standard reply code. A full reply that starts with 4 is retried. One that starts with 5 is final.
Who is at fault
Recipient
The address, the mailbox, or the recipient’s own mail rules.
Severity
WarningMailbox Full
Check the replyuser is overquota

iCloud storage is shared across email, backups, and files. When usage hits the limit, mail is temporarily rejected until space is freed.

Next steps

  1. 1Retry for a few days; most recipients will free space quickly.
  2. 2Pause marketing mail for that contact if the issue persists for weeks.
  3. 3Offer alternate channels (SMS, app notification) for time-sensitive notices.
  4. 4Encourage high-value contacts to upgrade storage or clean their mailbox.
Apple Mail (iCloud) documentation

More Apple Mail (iCloud) codes.

Full Apple Mail (iCloud) playbook

Other Apple Mail (iCloud) fixes

421 4.7.1Rate limitingRetrying
550 5.1.1User does not existFinal
550 5.1.1Inactive accountFinal
554 5.7.1 [HME1]Authentication failureFinal
554 5.7.1DMARC failureFinal
550 5.7.0Proofpoint blockFinal

In the glossary

Bounce (Hard)Hard bounce is when an email cannot be delivered because the address is invalid or blocked. It is a permanent failure and the address should be removed from your list.
Bounce (Soft)A soft bounce is when an email fails to deliver for a temporary reason, like a full inbox or a short outage at the recipient mail server. The address is still valid, and the email may be delivered if you try again later.
DeferralA deferral is when a receiving email server temporarily refuses a message but suggests trying again later.

Browse all raw Apple replies →

More references.

SMTP field manual.

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