Microsoft 365 530 5.7.57 "Client Was Not Authenticated": Fix the Device or App
530 5.7.57 is Microsoft 365 refusing mail from a device or app that connected to smtp.office365.com without signing in. The text reads "Client was not authenticated to send anonymous mail during MAIL FROM." It is not about the recipient. The fix is in the device or app's SMTP settings.
The 530 5.7.57 code page has the short version.
Reading the code
| Part | Value | Meaning |
|---|---|---|
| Reply code | 530 | Authentication required |
| Class | 5 | Permanent failure |
| Subject | 7 | Security or policy status |
| Detail | 57 | Microsoft's detail for an unauthenticated client |
The reply code and class follow RFC 5321 and RFC 3463. The detail 57 is Microsoft's own, so rely on the text.
Why it happens
- A printer, scanner or app is set to send through smtp.office365.com without credentials.
- Authentication is configured, but on the wrong port or without TLS.
- SMTP AUTH is disabled for the mailbox or for the whole tenant.
A longer variant reads "530 5.7.57 Client not authenticated to send mail. Error: 535 5.7.139 Authentication unsuccessful", which points at the credentials or the tenant setting.
Fix
- Configure the device with the mailbox's full credentials, port 587 and STARTTLS.
- Ask an admin to confirm that authenticated SMTP is allowed for the mailbox. The Microsoft 365 SMTP AUTH checker helps with the tenant side.
- For devices that cannot authenticate, use Microsoft's direct send or a connector instead.
- Look up the right server settings with the SMTP settings lookup.
Microsoft 365 SMTP auth and basic auth for cold email goes into why this setting matters for anyone sending through a Microsoft mailbox.
Related codes
The same family of connection problems includes 535 5.7.8 for bad credentials. If the recipient's side is rejecting you instead, see Outlook bounce codes.
What it does not tell you
Nothing about your list is involved. Do not suppress recipients because of a 530. What the device sends once it works is another matter: Microsoft 365 mailboxes have sending limits and are a poor home for bulk mail, which is covered in Microsoft 365 restricted sender.
Keep the address side clean
This code does not come from your list, but every bounce still counts against your sending reputation, so the addresses you do send to should be real. Upload your list on the verify page: the first 100 email checks are free with a Google sign-in, no card. Each address comes back valid, risky or invalid with a reason such as "Mailbox not found" or "Accepts all addresses", and nothing is sent to anyone on the list. For larger or recurring lists, see bulk email verification, list cleaning and pricing.
Common questions
What does 530 5.7.57 mean?
Microsoft 365 refused mail from a device or app that connected to smtp.office365.com without signing in. The text reads Client was not authenticated to send anonymous mail during MAIL FROM.
Is 530 5.7.57 a bounce?
No recipient was judged. It is a rejection of your connection, so it is a setup problem on the device or app.
What are the right settings?
Use the mailbox's credentials, port 587 and STARTTLS. For devices that cannot authenticate, use Microsoft's direct send or a connector.
Can SMTP AUTH being disabled cause it?
Yes. SMTP AUTH can be disabled for the mailbox or for the whole tenant, so ask an admin to check that authenticated SMTP is allowed.
Check your list before you send
Real mailbox checks over SMTP, and nothing is sent to the address. Sign in with Google and your first 100 email checks are free, no card. Plans for bigger lists are on the pricing page.