Bounce codes › Microsoft 365
550 5.7.133: Sender not authenticated for group
You wrote to a group address that only accepts mail from inside its own organisation. This is the default for new groups in Microsoft 365.
Only the recipient side can fix it Refused by a rule on the recipient side
This group address only accepts mail from inside its own organisation.
- Sent by: Microsoft 365 / Outlook
- Permanent (hard bounce). Sending the same message again fails again.
How Microsoft 365 words it (source):
Sender not authenticated for group
Why it happens
- The address is an internal distribution list such as
team@orsales-emea@. - The organisation never switched on "allow external senders" for the group.
What to do
- Write to a person at the company, not to the group.
- If the group is meant to take outside mail (a
support@orinfo@address), tell the company: their administrator or the group owner can allow external senders. - Remove the address from mailing lists. It will bounce every time.
Don't confuse it with
550 5.7.134 is the same rule on a single mailbox, and 550 5.7.12 is the general form. 550 5.7.124 is a group with a named list of allowed senders.
Questions
Does the address exist?
Yes. It is a working group, closed to outsiders.
Can I fix it from my side?
No. Only the recipient's organisation can open the group to external senders.
Got a different bounce?
Paste the whole message into the bounce code lookup. It reads the code and the words and tells you whose move it is.
Related codes
550 5.7.124Sender not in allowed-senders list (Microsoft 365)