The receiving mail system has run out of storage space. This affects all mailboxes on the server, not just one recipient. It is a server-side issue that the administrator must resolve.
What Does Error 4.3.1 Mean?
Enhanced status code 4.3.1 indicates the entire mail system (not just one mailbox) is out of storage. This means no emails can be delivered to any recipient on that server until the storage issue is fixed. This is more serious than individual mailbox quota issues.
This error is typically seen with smaller hosting providers or self-hosted mail servers. Major providers like Gmail and Microsoft virtually never run out of system-level storage.
Common Causes
- Server disk partition is full
- Mail queue consuming excessive storage
- Log files filling available disk space
- Backup processes consuming storage
How to Fix Error 4.3.1
- Wait for automatic retry - this is a server-side issue
- Contact the recipient organization postmaster if it persists
- Your MTA will retry over the next 24-48 hours
Frequently Asked Questions
Bounce code 4.3.1 means the recipient's entire mail server has run out of disk space or system resources and cannot accept any new messages. Unlike 4.2.2 (individual mailbox full), 4.3.1 indicates a server-wide storage problem affecting all users on that system. This is a temporary error that must be resolved by the recipient's server administrator by freeing disk space or adding storage capacity.
Error 4.2.2 means a specific recipient's mailbox is over its individual storage quota, while 4.3.1 means the entire mail server system has insufficient resources. With 4.2.2, other users on the same server can still receive email, but with 4.3.1, the server cannot accept mail for anyone. Both are temporary errors, but 4.3.1 requires server administrator intervention while 4.2.2 can be resolved by the individual user.
As a sender, you cannot fix this error -- it requires action by the recipient's mail server administrator. Your sending server will automatically retry delivery for several days. If the message is urgent, contact the recipient through an alternative channel. For administrators receiving this error on their own server, free disk space immediately, check that the transport queue partition has at least 4 GB available (for Microsoft Exchange), and set up automated cleanup of old logs, queue files, and transient data.