Delivery status codes from the Footer365 relay
Every temporary (4xx) and permanent (5xx) response the Footer365 relay can give Exchange Online, what each means, what to do, and how to find them in a message trace.
When Exchange Online hands a message to the Footer365 relay, the relay answers with an SMTP status code. Almost every message gets 250 (accepted and handed back to your Exchange). This article covers everything else.
If your organisation uses the Outlook add-in only, no message is handed to the relay, so none of these codes can occur. Using the Outlook add-in only
The first digit is what matters most:
- 4xx (temporary). Exchange keeps the message in its queue and tries again. Nothing is lost, but delivery is delayed until the condition clears.
- 5xx (permanent). Exchange stops trying and sends the sender a non-delivery report (NDR).
The relay never permanently rejects mail your organisation actually sent because of the state of your Footer365 account. A suspended, disabled or half-configured account has its mail delivered unsigned, not bounced. The permanent rejections below are for mail Footer365 cannot tie to your organisation.
Temporary responses (Exchange retries)
| Response | What it means | What to do |
|---|---|---|
451 4.3.2 Footer365 could not look up the tenant for this sender domain, try again later |
The relay could not reach the Footer365 service to find out whose domain this is. | Nothing; Exchange retries. Check the status page. |
451 4.4.4 This sender domain is served by a Footer365 relay in another region |
Your mail reached a relay in a different region from your account. A routing fault. | Contact support. |
451 4.3.5 No Exchange delivery host is recorded for this tenant, try again later |
Footer365 knows the message is yours but has nowhere recorded to return it to, usually because setup did not finish. | See Setup did not finish, or contact support. |
451 4.3.5 This sender domain is registered to more than one Footer365 tenant, try again later |
Two Footer365 accounts both list this domain, so the relay will not guess whose mail it is. | Contact support. |
451 4.3.5 Footer365 cannot verify mail for this tenant until its configuration is corrected, try again later |
Your account's Microsoft tenant identifier needs correcting before the relay can check your mail. | Contact support. |
451 4.3.2 This delivery report could not be matched to a Footer365 tenant, try again later |
A delivery report or read receipt whose author domain is not a domain Footer365 knows. | Contact support if it persists. |
451 4.7.1 Footer365 could not verify that this delivery report came from the organisation that owns its domain |
A delivery report failed the check that it came from your organisation. Reports are held rather than refused. | Contact support if it persists. |
451 4.3.0 Footer365 could not process this message, try again later |
An unexpected processing error, before the message could be handed back. | Nothing; Exchange retries. Contact support if it persists. |
452 4.3.1 Insufficient system storage, try again later |
The relay server was busy and asked Exchange to retry. | Nothing; Exchange retries. |
421 4.3.2 Service temporarily unavailable. The IP allowlist is not current; please retry in 5 minutes. |
The relay could not confirm the connection came from Exchange Online. | Nothing; Exchange retries. |
Permanent responses (sender gets an NDR)
| Response | What it means | What to do |
|---|---|---|
550 5.7.1 Relaying denied: no Footer365 tenant is configured for this sender domain |
The sender's domain is not one of the domains Footer365 holds for any account. Footer365 learns your domains from Microsoft 365 by sync, so this can happen for a domain added to Microsoft 365 very recently. | Contact support with the domain. |
550 5.7.1 Footer365 could not verify that this message was sent by the organisation that owns its sender domain |
The message did not prove it came from your Microsoft 365 organisation. Usually another organisation trying to send as your domain through the relay; for genuine mail, it means the Footer365 transport rule has been altered. | If the sender was genuinely one of yours, contact support and do not edit the Footer365 rules. |
552 5.3.4 Message too large, 552 5.3.4 Message size exceeds fixed maximum message size or 552 5.3.4 Message line too long |
The message exceeded the relay's size limit, or contains a line longer than it accepts. The Footer365 rules leave messages over 24 MB to Exchange, which sends them unsigned, so a size refusal means the rule's size exception has been removed or edited. | Contact support with the message details, and do not edit the Footer365 rules: the daily check puts the exception back. |
Finding these in a message trace
- In the Exchange admin centre, go to Mail flow, then Message trace.
- Search for the sender, a recipient and the time range.
- Open the message and look at its events. A deferred message shows a defer event whose detail includes the relay's response text. A message that bounced shows a failure with the response text in the NDR.
- Messages still waiting are also listed in the Queued messages report in the Exchange admin centre.
For Microsoft's own description of message trace, see Message trace in the Exchange admin centre.
When you contact support, include the full response text, the sender, one recipient and the approximate time. If the delivered message is available, its X-Footer365-Relay-Id header identifies the relay's own record.
Related
Still stuck?
Tell us what you were trying to do and what you saw. Include the sender, a recipient and roughly when a message was sent, and we can trace it.