Generic SMTP delivery response
Understand SMTP 5.1.6: Mailbox moved without forwarding address
The destination mailbox used to exist, but the receiving system no longer accepts mail for it and supplied no forwarding address.
A representative response is:
550 5.1.6 Mailbox moved without forwarding address.
This is permanent for the old address. Find and use the current recipient address.
What this response means
Standard 5.1.6 Destination mailbox has moved, no forwarding address means the old recipient is no longer deliverable. Retrying the same address will not help.
Fix it
- Contact the person or organization through another trusted channel and request the current address.
- Update contacts, CRM records, invoices, account profiles, and automation at the original source.
- Remove or suppress the obsolete address from mailing lists.
- If you operate the receiving domain and the move was unintended, restore the alias or add an approved forwarding path.
- Send a new message only after the destination is corrected.
Do not guess a new address and do not treat the old mailbox as a temporary failure.
Who can fix it
The sender can update its records; the receiving-domain administrator can restore or redirect the old address if policy allows.
Related troubleshooting
Use 5.1.1 guidance when the receiver simply says the mailbox never existed.
Frequently asked questions
What does SMTP 5.1.6: Mailbox moved without forwarding address mean?
The mailbox was valid in the past but no longer accepts mail, and the receiving system has no forwarding address to return.
Can MailFixIt prove this entire bounce from public DNS?
No. The current checker can evaluate selected public DNS configuration, but it cannot recreate recipient state, credentials, reputation, message content, or a historical provider SMTP decision.
Related email diagnostics
Primary sources: IANA SMTP Enhanced Status Codes.