5.7.64 TenantAttribution; Relay Access Denied
5.7.64 TenantAttribution; Relay Access Denied
Authentication is not the problem here - the message was accepted and then could not be attributed to a connector that permits relay. Classic after a device’s public IP changes, after a certificate on an inbound connector is replaced, or when a smart-host setup is moved to a new network. Check which connector should be matching this traffic and what it matches on, rather than the mailbox credentials.
Check it from the machine that is failing
npx zerosmtp-check --explain "5.7.64 TenantAttribution; Relay Access Denied"
No install and nothing sent. It reads the refusal your own client printed - which is rarely what the server said, because libraries and device panels rewrite it - and says which of these cases you are in.
If the send is hanging rather than being refused, the cause is usually the network and not the credentials. npx zerosmtp-check with no arguments checks ports 25, 587 and 465 from where you are standing.
This is not the Basic auth shutdown
Authentication worked. Do not change the authentication settings — the problem is the From address.
- Check what address the device or application puts in
From. - Check which mailbox the credentials belong to.
- If they differ, either set
Fromto the authenticated mailbox, or grant that mailbox Send As on the address you want to use.
This turns up most often after pointing a device at a shared or service mailbox and leaving the old From address in its settings.
Two things this is often confused with
| Symptom | Actual cause |
|---|---|
| Connection times out; no authentication error ever appears | The network is blocking outbound SMTP. Cloud providers block port 25 and often 587 by default — see troubleshooting. |
Certificate verify failed / unable to get local issuer certificate | The device’s trust store cannot validate the server certificate. Common on firmware predating current root CAs — see the Canon Maxify MB2755 case. |
Source: Microsoft’s own list of Exchange Online error codes. This entry was written from that documentation rather than from watching a machine fail, which is worth knowing when you compare it against what your hardware actually printed.
Related
- All SMTP AUTH error messages
- Which devices have OAuth firmware
- What breaks at the end of December 2026
Seeing a string that is not here? Report it with what produced it. Errors from real hardware are worth more than anything transcribed from documentation.
Last reviewed 2026-08-16.
Updated 22 Aug 2026