452 4.2.2: Mailbox full (temporary)
452 4.2.2 means the recipient's mailbox is full at the moment. The 4 says the failure is temporary, so the server may accept the message later. If it repeats for days, the mailbox is probably abandoned.
- Bounce type
- Soft bounce (temporary)
- Usually caused on
- The recipient's side
- Terlido report label
- Mailbox full
What the standard says
RFC 5321 defines 452 as "insufficient system storage": the server did not take the action because it ran out of space. RFC 3463 defines X.2.2 as "Mailbox full". With class 4 (persistent transient failure) in front, the sender is told to try again later, in contrast to 5.2.2 where the failure is final.
What the mailbox providers say
- Gmail (452 4.2.2): “The recipient's inbox is out of storage space...” Source
Common causes
- A recipient who is away and whose inbox filled up while they were gone.
- A mailbox that is close to its limit and only rejects larger messages.
- A mailbox that nobody reads anymore and that will stay full.
- A temporary storage problem on the receiving server, which is not tied to this one recipient.
- A mailbox on a small plan with a low storage limit, where one large message tips it over.
How to fix it
- Do nothing for a single occurrence. A soft bounce is expected to clear, and your sequence moves on to its next step.
- If the same contact keeps returning this code across several steps, take them out of the sequence by hand.
- Keep messages small. A near-full mailbox may take a short text message and refuse a heavy one.
- Review soft bounce reports weekly, so repeat cases do not sit unnoticed in the list.
- Check whether other contacts at the same company also return full-mailbox codes. If they do, the cause may be a server setting, and you can wait.
- Mark contacts that return this code more than once in a sequence, and remove them before the next step goes out.
Is it a deliverability problem?
A temporary full-mailbox code is not a deliverability problem on its own. It becomes a data quality signal when it repeats for the same contact, because the mailbox is then likely abandoned. At that point it will turn into a permanent 5.2.2 failure or silence, and the contact has no value. Soft bounces do not stop a sequence, which is useful for short problems and a waste for long ones. Each further step to a full mailbox adds nothing to your replies and adds a little noise to your reports, so a short manual review pays off.
How Terlido handles it
When a bounce message for this code arrives in a connected mailbox, Terlido reads the status code. An enhanced code that starts with 4 is a soft bounce. In the campaign Reports tab this one is grouped as "Mailbox full".
On a soft bounce Terlido logs the event on the lead's activity. The lead is not stopped, and the sequence continues at its next scheduled step.
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Related error codes
- 552 5.2.2: Mailbox full
- 451 4.3.0: Temporary mail system problem
- 550 5.2.1: Mailbox disabled or not accepting mail