5.7.133: The group or mailbox takes no mail from outside (Microsoft 365)

At a glance

• Type: permanent failure (class 5, RFC 3463 §2). The sending server does not retry; sending the same message again fails the same way until the cause is fixed.
• Basic code: varies; the enhanced code is the part that identifies the problem.
• Enhanced code 5.7.133: not in the IANA registry; the group is security or policy status (RFC 3463 §3.8).
• Who uses it: Microsoft (Exchange Online): sender not authenticated for the group, mailbox or mail user.

A 5.7.133 bounce from Microsoft 365 means the group you wrote to accepts mail only from people inside its own organization. Your message came from outside, so it was refused. Close relatives of this code cover mailboxes, public folders and mail users.

What it means

These are Microsoft's codes, not ones from the IANA registry. Microsoft's Exchange Online NDR reference describes each one as a sender that is not authenticated for that recipient, because the recipient is set to reject mail from outside the organization:

• 5.7.133: a group.
• 5.7.134: a mailbox.
• 5.7.13 and 5.7.135: a public folder.
• 5.7.136: a mail user.

"Not authenticated" here does not mean your SPF or DKIM failed. It means you are not a signed-in member of the recipient's organization, which is the only kind of sender this recipient accepts.

Common causes

• The group is meant for internal use, and its setting to accept only internal senders is on.
• You are a partner, customer or former employee writing to an internal list.
• You are inside the organization but sent from a personal or external account.
• A form, CRM or ticket system sends from outside the tenant to an internal-only group.

How to fix it

If you are the sender:

1. Check whether you meant to write to a public contact address instead of an internal group.
2. If you also have an account in the recipient's organization, send from that account.
3. Ask a contact inside the organization to forward your message, or to ask their admin to open the group to outside senders.

If you run the recipient's organization:

1. Find the group, mailbox or public folder in the Exchange admin center.
2. In its delivery settings, allow senders from outside the organization, or keep it closed if internal-only is what you want.

Only the recipient's admin can change this. Nothing in the sender's setup fixes it.

Similar refusals

A group that accepts only a list of named senders gives 5.7.124. An organization that blocks its own users from forwarding mail outside gives 5.7.520. Many other policy refusals use 550 5.7.1.

What to do with the address

Keep it. The address exists and works; it is closed to outside mail.

Related codes

• 5.7.124: Sender not in the group’s allowed senders (Microsoft 365)
• 550 5.7.1: Delivery not authorized: refused for policy reasons
• 5.7.520: External forwarding is not allowed (Microsoft 365)

See every bounce code in the dictionary.

Many bounces from addresses that do not exist can be avoided: check an address with our free email checker, or clean a whole list before you send.

How we wrote this: drafted by the email-validation.org team with the help of AI writing tools, from our product documentation and the sources linked in the text.