550 5.7.135: public folder rejects mail from outside
The recipient is a mail-enabled public folder set to reject messages from senders outside its organization.
- Microsoft
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.7.135
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The recipient's side. Their mail admin has to change something; you can tell them.
- What the server says
550 5.7.135 Sender was not authenticated for public folder
What it means
Microsoft covers 550 5.7.13 and 550 5.7.135 in one article for a public folder that rejects external senders; its error table describes the code as Sender was not authenticated for public folder. The folder requires all senders to be authenticated, so outside mail fails. Only an admin of the receiving organization can change this, by allowing all senders in the folder's mail flow settings or by adding specific external senders, represented by mail contacts or mail users, to the folder's allowed senders list.
Common causes
- The public folder requires all senders to be authenticated.
- The folder is meant to receive internal mail only.
How to fix it
- 01Ask the receiving organization's admin to allow your address.
- 02Admins: in Public folders, open the folder's mail flow settings, clear Require that all senders are authenticated and choose All senders.
- 03Or choose Only senders in the following list and add the external senders as mail contacts, plus a group containing your internal users.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Fix NDR error "550 5.7.13" or "550 5.7.135" in Exchange Onlinelearn.microsoft.com
- Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
Related codes
- 550 5.7.13No permission to post to the public folder.Delivery to a mail-enabled public folder failed because the permission the sender falls under does not allow creating items in it.
- 550 5.7.1Public folder does not accept external mail.An external sender wrote to a mail-enabled public folder in Microsoft 365, which by default accepts mail only from authenticated senders.
- 5.7.12Recipient accepts mail only from its organization.The address you wrote to takes mail only from inside its own organization, so outside senders are refused until that organization's admin changes the setting.
Further reading
All 111 Microsoft codesEvery code in the wikiPaste your own bounce