Enhanced Status Code 4.4.7: Delivery Time Expired

Temporary failure High severity Network RFC 3463

What it means

Enhanced Status Code 4.4.7 means “Delivery Time Expired.” Your email has been sitting in the retry queue for too long and the maximum delivery time has expired. The sending server tried repeatedly to deliver the message but failed every attempt over the configured retry period (typically 24-72 hours).

At a glance

Code4.4.7

Bounce typeSoft (temporary)

SeverityHigh

CategoryNetwork

What to doQueued and retried automatically

StandardRFC 3463

What it looks like in your mail logs

Action: failed Status: 4.4.7 Diagnostic-Code: smtp; 451 4.4.7 Queue.Expired; message expired, the server was unable to deliver the message before the retry period ended

What does 4.4.7 mean?

Enhanced status code 4.4.7 indicates your sending server has exhausted its retry attempts for this message. After receiving temporary failures (4xx codes) from the recipient server, your MTA kept retrying according to its schedule. When the maximum retry period expired (typically 24-72 hours depending on your MTA configuration), the message was bounced with 4.4.7.

This is a significant error because it means the recipient server was unreachable or rejecting messages for an extended period. While technically a soft bounce, the practical impact is that the message was never delivered. The underlying cause might be any of the 4xx temporary errors (421, 450, 451, etc.) that persisted for too long.

Microsoft 365 commonly returns 4.4.7 when the recipient server has been unreachable for the retry period. Check whether the recipient domain MX records are correct and the destination server is operational.

How 4.4.7 plays out

Your server attempts delivery

The recipient defers with a temporary 4.4.7 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 4.4.7 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
4.4.7 is	✓ this code

Common causes of 4.4.7

Recipient server was down for an extended period exceeding your retry timeout
Persistent soft bounces (421, 450, 451) that never resolved
DNS changes that made the recipient server temporarily unreachable
Network routing issue that persisted through the entire retry period
Rate limiting so severe that no retry window was available

How to fix 4.4.7

Check if the recipient domain is currently reachable and accepting mail
Verify recipient MX records are valid and pointing to active servers
Consider increasing your MTA retry period if messages are timing out too quickly
Retry sending manually after confirming the recipient server is available
If the recipient server is back online, resend the message

Frequently asked questions

What does error 4.4.7 "delivery time expired" mean?

Error 4.4.7 means your email server attempted to deliver a message over an extended period but the recipient's server never accepted it, and the retry window has expired. The sending server queued the message and retried multiple times (typically over 24 to 48 hours), but the destination server was consistently unreachable, unresponsive, or refused the connection. The message is returned to the sender as undeliverable.

How many days does Exchange retry before returning 4.4.7?

Microsoft Exchange Online retries delivery for 24 hours (1 day) before returning a 4.4.7 non-delivery report. On-premises Exchange Server defaults to 2 days (48 hours), though administrators can customize this value. The retry interval and message expiration timeout can be configured in the Transport service settings. Gmail and other providers have their own retry windows, typically ranging from 12 to 72 hours.

How do I fix the 4.4.7 message expired error?

Since this error indicates the recipient's server was unreachable, first verify the recipient's email address is correct. Check if the recipient's domain has valid, functioning MX records using an MX lookup tool. If the records are correct, the recipient's mail server may be experiencing downtime or network issues; wait a few hours and try again. If the problem persists, contact the recipient through another channel to alert them to a potential server issue on their end.

What is the difference between 4.4.7 and 5.4.7?

Both codes relate to delivery timeout, but 4.4.7 is a temporary failure notification (the server is still retrying), while 5.4.7 is the final permanent failure after all retries have been exhausted. You may receive a 4.4.7 delay notification while the server is still attempting delivery, followed by a 5.4.7 non-delivery report when the retry window expires. The causes are the same, an unreachable destination server, but 5.4.7 is the definitive "message could not be delivered" notification.

Related bounce codes

Sources & further reading

RFC 3463 · The standard that defines this reply code Email nondelivery reports and SMTP errors in Exchange Online · Microsoft reference for the 4.4.7 message expired NDR Configure message retry, resubmit, and expiration intervals · Microsoft doc on the Exchange retry window that triggers 4.4.7

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