Permanent failure — do not retry
SMTP 550 5.7.124
sender not in allowed senders list (Microsoft 365)
SMTP 550 5.7.124 means you sent to a Microsoft 365 distribution group that only accepts mail from listed senders, and you are not on that list. The group exists; its owner has restricted who can post to it. Only the group owner or an admin can change that.
How it appears
550 5.7.124 Sender not in allowed-senders list
What causes it
- The group only accepts mail from members or a named list of senders.
- The group does not accept mail from outside the organisation.
- You sent from a different address than the one the owner allowed.
How to fix it
In order — try the first one first.
- Ask the group owner to add your address to the allowed senders, or to allow external senders.
- Write to a named person instead of the group.
- Do not retry. It will fail until the setting changes.
Common questions
- What does SMTP 550 5.7.124 mean?
- SMTP 550 5.7.124 means you sent to a Microsoft 365 distribution group that only accepts mail from listed senders, and you are not on that list. The group exists; its owner has restricted who can post to it. Only the group owner or an admin can change that.
- Should I retry a 550 5.7.124 error?
- No. 550 is a permanent failure, so the message will never be delivered no matter how many times you try. Remove the address — repeated sends to permanent failures are one of the main signals mailbox providers use to throttle a sender.
- How do I fix SMTP 550 5.7.124?
- Ask the group owner to add your address to the allowed senders, or to allow external senders.
Other 550 replies
- 550 5.1.1 — mailbox does not exist
- 550 5.7.1 — message refused by policy
- 550 5.4.1 — recipient address rejected, access denied
- 550 5.2.1 — mailbox disabled, not accepting messages
- 550 — mailbox unavailable
- 550 5.1.0 — address rejected, other address status
- 550 5.1.10 — recipient not found (Microsoft 365)
- 550 5.1.8 — bad outbound sender (Microsoft 365)
- 550 5.4.5 — daily sending limit exceeded (Gmail)
- 550 4.4.7 — message expired in the queue
- 550 5.7.25 — no PTR record for sending IP (Gmail)
- 550 5.7.26 — blocked, sender unauthenticated (Gmail)
- 550 5.7.27 — SPF authentication failed (Gmail)
- 550 5.7.28 — unusual rate of unsolicited mail (Gmail)
- 550 5.7.23 — SPF violation (Microsoft 365)
- 550 5.7.509 — DMARC failed, policy reject (Microsoft 365)
- 550 5.7.606-649 — banned sending IP (Microsoft)
- 550 5.7.705 — tenant has exceeded threshold (Microsoft 365)
- 550 5.7.708 — traffic not accepted from this IP (Microsoft 365)
- 550 5.7.750 — blocked from sending from unregistered domains (Microsoft 365)
- 550 5.7.515 — authentication required for high-volume senders (Outlook.com)
- 550 5.7.1 S3140 — IP range on Outlook.com block list
Last reviewed 2026-09-11