Enhanced Status Code 5.1.6: Destination Mailbox Has Moved

Permanent failure Medium severity Address RFC 3463

What it means

Enhanced Status Code 5.1.6 means “Destination Mailbox Has Moved.” The recipient mailbox has been permanently moved to a new address and the server does not automatically forward mail. Update your records with the new address provided in the bounce response.

At a glance

Code5.1.6

Bounce typeHard (permanent)

SeverityMedium

CategoryAddress

What to doSuppress the address; do not retry

StandardRFC 3463

What it looks like in your mail logs

Remote Server returned '550 5.1.6 RESOLVER.ADR.RecipMoved; recipient moved'

What does 5.1.6 mean?

Enhanced status code 5.1.6 indicates the recipient mailbox existed at one time but has been permanently relocated to a different address. Unlike a temporary redirect, this is permanent. Some servers include the new address in the bounce response.

This code is seen during organizational email migrations, domain changes, or when users move to a new email provider. If the bounce response includes a new address, update your records. Otherwise, contact the recipient through another channel for their current address.

How 5.1.6 plays out

Your server attempts delivery

The recipient server returns a permanent 5.1.6 rejection

This is a hard bounce: the message will not be accepted as sent

Suppress the address and fix the root cause before resending

Where 5.1.6 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
5.1.6 is		✓ this code

Common causes of 5.1.6

Recipient changed email providers
Organization migrated to a new email domain
Mailbox was merged with another account
User left the organization and forwarding has expired

How to fix 5.1.6

Check the bounce response for the new forwarding address
Update your records with the new address if provided
Contact the recipient through another channel for their current email
Remove the old address from your list

Frequently asked questions

What does bounce code 5.1.6 "Destination mailbox has moved" mean?

Bounce code 5.1.6 means the recipient's email address was valid at one time, but the mailbox has been relocated to a new address and automatic forwarding is not configured. This is a permanent delivery failure indicating you need to obtain the recipient's new email address. The old address is no longer accepting mail and will not forward messages to the new location.

How do I fix a 5.1.6 email bounce?

Contact the recipient through an alternative method (phone, social media, or another known email address) to obtain their current email address. Update the address in your contacts, mailing lists, and any automated systems. If you are a mail administrator receiving this error for users in your organization, verify that proper mail forwarding rules are configured in your mail server to redirect messages from old addresses to new ones.

Why does the recipient's mailbox show as "moved"?

A mailbox is marked as "moved" when an email account has been migrated to a different server, domain, or email provider without setting up forwarding. This commonly happens during company mergers, email system migrations (such as moving to Microsoft 365 or Google Workspace), employee transfers, or domain changes. The old server knows the address existed but can no longer deliver to it and no forwarding rule is in place.

Related bounce codes

Sources & further reading

RFC 3463 · The standard that defines this reply code Microsoft Learn, Cannot send messages to a moved mailbox · Exchange article describing NDRs returned after a mailbox is moved without a routing address.

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