Email error

Question

People that are emailing me say that they get an message that there is an error in delivering the email to my email address. How can this be fixed?

Answer 1

Hello

Is it possible to find out what the bounce email says exactly? It contains important diagnostic data that helps shed some light of the root cause. Feel free to redact personal information when you share.

In addition, can you tell me, did you receive their emails regardless, or don't they come in at all?

Any chance these are yahoo or gmail senders?

Answer 2

Delivery errors to an Outlook.com address usually come from either a problem with the sender’s message, the address they’re using, or the state of the Outlook.com mailbox. Use these steps to narrow it down and fix it.

1. Collect the exact error from senders

• Ask one of the people who can’t email the address to send (as text or screenshot) the full “delivery failed” / Non-Delivery Report (NDR) they receive.
• The wording in that report (for example, “mailbox full,” “user unknown,” “host unknown,” “blocked,” etc.) identifies the cause and the right fix.

2. Confirm the email address is valid and typed correctly

Many NDRs are caused by an incorrect or non‑existent address.

• Errors like “Mailbox not found,” “Invalid mailbox,” “User unknown,” “Mailbox unavailable,” “Host unknown,” or “Domain lookup failed” indicate the address or domain is wrong.
• Ask senders to:
  • Remove the address from their auto‑complete / address cache.
  • Re‑enter the full Outlook.com address manually, checking spelling and domain (for example, @outlook.com vs @outlook.co.uk).
• If the address was ever changed or removed as an alias, it may no longer exist; in that case, messages to it will always fail.

3. Check that the Outlook.com mailbox is active and accessible

• Sign in to Outlook.com with the affected address.
• If sign‑in fails or the mailbox does not open, the mailbox may be disabled or removed. In that situation, messages to it will bounce for all senders.
• For work/school (Microsoft 365) accounts, a disabled mailbox must be re‑enabled by the organization’s administrator before mail can be delivered again.

4. Check for “mailbox full” or quota errors

If senders see “Mailbox full” or “Quota exceeded”:

• Sign in to Outlook.com and reduce mailbox size:
  • Delete unneeded messages (especially with large attachments) from Inbox, Sent Items, Junk Email, and Deleted Items.
  • Empty Deleted Items.
• After freeing space, ask the sender to resend the message.

5. Look for temporary server or routing issues

Some errors indicate a temporary problem between mail servers:

• Examples: “Can’t connect to remote server,” “Connection timed out,” “No adequate servers,” “message expired,” “Out of memory,” “Resources temporarily unavailable.”
• These typically resolve on their own. If the NDR says the recipient’s provider will keep trying, no action is needed.
• Otherwise, the sender should wait a bit and try sending again.

6. Check if the sender is being blocked as spam

If the NDR mentions “blocked” or “listed in” and references sites like “spamcop,” “spamhaus,” or similar:

• The sender’s mail server or account is being treated as a spam source by the receiving system.
• The fix must be done on the sender’s side: they need to contact their email provider’s support and request removal from the blacklist or investigate why their mail is being flagged as spam.

7. Verify rules and forwarding on the Outlook.com account

If Outlook.com is forwarding messages or applying rules, misconfigured settings can cause NDRs:

• Sign in to Outlook.com and review:
  • Mail rules that move or forward messages.
  • Forwarding settings (for example, forwarding to an address that no longer exists).
• If forwarding points to an invalid address, messages may bounce. Correct or disable such forwarding.

8. For Microsoft 365 / Exchange Online error 5.7.1

If the NDR includes 5.7.1:

• This usually means a permission or routing issue, such as:
  • No permission to send to the mailbox or distribution group.
  • No permission to send through an intermediate server.
  • Message routed to the wrong server.
• The organization’s Microsoft 365/Exchange admin must adjust permissions or routing according to the guidance for error 5.7.1.

9. If problems persist

• Capture one complete NDR from a sender (including error code and text).
• Provide that NDR to Microsoft support or the relevant email provider’s support so they can identify the exact cause and apply a targeted fix.

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References:

• Sent email in Outlook.com comes back "delivery failed"
• Failed delivery messages from the postmaster at outlook.com, microsoft.com, or service.microsoft.com
• Office 365 email delivery error 5.7.1
• I receive a 550, 553, or relay-prohibited error when sending email messages