550 5.7.124: Microsoft sender not in allowed list
550 5.7.124Sender not in allowed senders listPermanent: retrying will not helpFrom Microsoft 365 and Outlook.com
550 5.7.124 Sender not in allowed-senders list
What it means
Exchange lets a group or mailbox owner list exactly who may send to it, using the setting that only accepts messages from specific senders or members. Your address is not on that list, so the resolver rejects the message with 5.7.124. The text usually reads like the example and may name the group.
This differs from the authentication codes. With 5.7.1 AuthRequired or 5.7.133 the group refuses all outside mail. With 5.7.124 the group may accept other external people; you specifically are not allowed. Internal senders can hit it too if they are not on the list.
Likely causes
- The group is a company wide announcement list that only a few people may post to.
- A moderated or restricted alias was set up to accept mail from one team only.
- You send from a different address (an alias or personal account) than the one on the list.
- A member was removed, or the allowed list references a group you are no longer in.
How to fix it
- Sender: check that you are sending from the address the group owner expects.
- Ask the group owner or admin to add your address to Delivery management, accepted senders.
- Recipient admin with PowerShell: Set-DistributionGroup allstaff -AcceptMessagesOnlyFromSendersOrMembers @{Add="user@example.com"}.
- If the restriction is no longer wanted, clear the list so the group falls back to its normal settings.
Checks that apply
- Email Header Analyzer Shows the envelope and From addresses you actually sent with, which must match the allowed list entry.
- MX Lookup Confirms the group’s domain is on Microsoft 365, where this Exchange setting applies.
FAQ
- Can I get around it by sending from another address?
- Only if that address is on the list. The check is on your sender address, so ask to be added.
- Is this the same as being blocked?
- No. It is a per group allow list. Mail to individual people at that company is unaffected.