SMTP Error 431: Not Enough Disk Space on Server

Temporary failure Medium severity System RFC 5321

What it means

SMTP Error 431 means “Not Enough Disk Space on Server.” 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.

At a glance

Code431

Bounce typeSoft (temporary)

SeverityMedium

CategorySystem

What to doQueued and retried automatically

StandardRFC 5321

What it looks like in your mail logs

431 4.3.1 STOREDRV.Deliver; disk is full and the server cannot accept new messages

What does 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.

How 431 plays out

Your server attempts delivery

The recipient defers with a temporary 431 reply

Your server queues the message and retries on a back-off schedule

It delivers on a later attempt, or becomes a hard bounce if it keeps failing

Where 431 sits: soft vs hard bounce

	Soft bounce (4xx)	Hard bounce (5xx)
Nature	Temporary	Permanent
SMTP class	`4xx`	`5xx`
What to do	Let it retry	Suppress the address
Recoverable?	Often	No
431 is	✓ this code

Common causes of 431

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 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

What does SMTP error 431 mean?

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.

How do I fix SMTP error 431?

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.

Is SMTP 431 a permanent or temporary error?

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.

Related bounce codes

Sources & further reading

RFC 5321 · The standard that defines this reply code RFC 3463 section 3.3 · Enhanced code X.3.1 (Mail system full), the status this maps to Microsoft Exchange transient delivery errors · How Exchange reports transient delivery failures such as STOREDRV disk-full conditions

Reviewed by Jennifer Jackson, Email Deliverability Analyst · June 2026 ← All bounce codes