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452 4.2.2 error: recipient's mailbox is full

452 4.2.2 means the recipient's mailbox is out of space. It's temporary and on their side: your server retries, and your domain isn't at fault.

Their mailboxSomething on their side, like a full mailbox. Usually not about you.

What 452 4.2.2 means

Gmail452 4.2.2 The recipient's inbox is out of storage space.

The mailbox is full right now.

List problem or sender problem?

Their mailbox. Only the recipient can free up space. It's a temporary failure: the sending server retries on its own, but repeated deferrals are a warning.

How to fix 452 4.2.2

  1. Let your server retry; it may deliver once they free up space.
  2. If it keeps failing, reach the person another way.
  3. Don't treat it like a dead address: a full mailbox alone isn't a reason to drop someone.

In SendingOS, 452 4.2.2 shows on the conversation with its reason and code, so a problem on their side never gets mistaken for one on yours.

Not sure whether a spike in bounces is the list or the domain? Read High email bounce rate? Burned domain or bad list.

552 5.2.2450 4.2.1

Sources: Google: Gmail SMTP errors and codes · RFC 3463