The receiving mail server has run out of disk space and cannot store incoming messages. This is a server-side issue that will typically be resolved by the server administrator.
What Does Error 431 Mean?
SMTP code 431 indicates the receiving mail server itself (not just the individual mailbox) has run out of disk space. This is different from error 422 (individual mailbox full) because 431 affects the entire server, meaning no one on that server can receive email until the issue is resolved.
This error is more common with self-hosted mail servers or smaller hosting providers than with large providers like Gmail or Microsoft. It is a server administrator issue and not something the sender can fix. Your sending server should retry automatically.
Common Causes
- Receiving mail server disk partition is full
- Log files consuming excessive disk space on the receiving server
- Server backup process filling storage
- Shared hosting environment with storage limits
How to Fix Error 431
- Wait and retry - this is a server-side issue for the recipient to resolve
- Contact the recipient organization postmaster if the issue persists for days
- Your MTA should handle automatic retries with exponential backoff
Frequently Asked Questions
SMTP error 431 means the recipient's mail server does not have enough disk space or system storage to accept your message. It is a temporary server-side error indicating the receiving server has run out of resources. Your sending server will typically retry delivery automatically. The issue must be resolved by the recipient's mail server administrator.
As a sender, you cannot directly fix SMTP 431 because it is a problem with the recipient's server storage. Wait 30-60 minutes and retry sending, as the issue is often temporary. If the problem persists, contact the recipient through an alternative channel and let them know their mail server is rejecting messages due to insufficient storage. Their server administrator needs to free up disk space or increase storage allocation.
SMTP 431 is a temporary error, meaning your email may be delivered successfully on a later attempt once the recipient's server storage issue is resolved. Most sending mail servers will automatically retry delivery for up to 3-5 days. If the problem is not resolved within that retry period, you will receive a final bounce-back notification indicating permanent delivery failure.