SMTP Error 422: Recipient Mailbox Storage Exceeded

Temporary failure Medium severity Mailbox RFC 5321

What it means

SMTP Error 422 means “Recipient Mailbox Storage Exceeded.” The recipient mailbox has exceeded its storage limit and cannot accept new messages. This is a temporary failure that may resolve when the recipient frees up space by deleting old emails.

At a glance

Code422

Bounce typeSoft (temporary)

SeverityMedium

CategoryMailbox

What to doQueued and retried automatically

StandardRFC 5321

What it looks like in your mail logs

422 4.2.2 The email account that you tried to reach is over quota and could not accept new messages

What does 422 mean?

SMTP code 422 indicates the recipient's mailbox has reached its storage quota and cannot accept additional messages. This is functionally similar to enhanced code 4.2.2 and is treated as a soft bounce because the condition may be temporary - the recipient might delete messages to free up space.

While individual 422 bounces are common and not alarming, consistently bouncing to the same address with 422 suggests the mailbox may be abandoned. After 3-5 consecutive soft bounces to the same address over several days, most email best practices recommend suppressing that address to protect your sender reputation.

How 422 plays out

Your server attempts delivery

The recipient defers with a temporary 422 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 422 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
422 is	✓ this code

Common causes of 422

Recipient mailbox has reached its storage quota
Mailbox is abandoned and has filled up over time
Recipient receives high volume of email without cleaning up
Organization has set restrictive mailbox size limits

How to fix 422

Retry delivery after a delay - the recipient may free up space
Suppress the address after 3-5 consecutive soft bounces over multiple days
Contact the recipient through another channel to alert them
Review your list for inactive addresses that consistently return 422

Frequently asked questions

What does SMTP error 422 mean?

SMTP error 422 means the recipient's mailbox has exceeded its storage limit and cannot accept new messages. The email server is rejecting your message because the specific recipient's account is over quota. This is a mailbox-level storage issue, not a server-wide problem. Your message will not be delivered until the recipient frees up space in their mailbox.

How do I fix SMTP error 422 "Exceeded storage allocation"?

As a sender, you cannot directly fix this error because the recipient's mailbox is full. Contact the recipient through an alternative channel (phone, text, or messaging app) and let them know their email storage is full. Suggest they delete old emails and empty their trash folder. You can retry sending after they have freed up space. If this is a recurring issue, consider sending smaller messages without large attachments.

Is SMTP 422 a temporary or permanent error?

SMTP 422 can be treated as a temporary error, since the delivery failure may resolve once the recipient clears mailbox space. However, most sending servers will not automatically retry 4xx errors indefinitely. If the recipient does not manage their storage within the retry window (typically 3-5 days), the message will permanently bounce. For marketing emails, repeated 422 errors from the same address indicate an inactive or abandoned mailbox that should be removed from your list.

Related bounce codes

Sources & further reading

RFC 5321 · The standard that defines this reply code RFC 3463 section 3.2 · Enhanced code X.2.2 (Mailbox full), the status this maps to

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