4.3.1: receiving system out of storage
The receiving mail server has run out of storage space, so it cannot accept messages for now; the sending server keeps the message and retries later.
- Standard
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 4.3.1
- Provider
- Standard SMTP codes
- Temporary or permanent
- TemporaryThe sending server keeps the message and tries again later.
- Who has to act
- The recipient's side. Their mail admin has to change something; you can tell them.
- What the server says
4.3.1 Mail system full
What it means
X.3.1 says the mail system as a whole, rather than one mailbox, has run out of storage. RFC 3463 notes that the individual recipient may not be able to free space, and calls the code useful only as a persistent temporary error, so 4.3.1 is the form you see. It often comes with reply code 452 (insufficient system storage). The sending server keeps the message and tries again, and once the receiving administrators free space, delivery goes through. If the condition lasts longer than the sending server's retry period, the message is returned as undeliverable. Some servers also send 4.3.1 when they are short of memory or other resources.
Common causes
- The receiving server's disk or queue storage is full.
- The server is short of other resources and refuses new mail until the load drops.
How to fix it
- 01Do nothing at first: the sending server retries on its own.
- 02If messages stay queued for long, tell the recipient so their administrator can free space.
- 03Recipient admins: free disk space on the mail server, check queue and log growth, and confirm it accepts mail again.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 452Insufficient system storage.The receiving server is short of storage or has hit a limit, such as the number of recipients in one message, and asks the sender to try again later.
- 5.2.2Mailbox full.The recipient's mailbox has reached its storage quota, so the server will not take more mail until the owner deletes messages or gets more space.
- 4.4.5Mail system congested.The mail system was too busy to deliver the message at that moment, so delivery is delayed and will be tried again.
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