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.
Should you remove the address?
Remove the address from your list
Remove it from outreach lists. The group won't accept your mail, and group addresses rarely suit cold or marketing sends anyway.
Block. Retrying changes nothing until the cause on your side is fixed.
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.
Who sends it
Microsoft 365 and Exchange Online.
Microsoft 365
Provider's description Sender not in allowed-senders list
Microsoft notes that even the group's owner may need to be added to the list to send to it.
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.
- Is 550 5.7.124 a hard bounce or a soft bounce?
- 550 5.7.124 is a block rather than a classic hard or soft bounce. The rejection is about your sending (authentication, reputation, content or the recipient's policy), not about whether the address exists. Retrying changes nothing until the cause on your side is fixed.
- Should I remove the address after a 550 5.7.124 bounce?
- Remove it from outreach lists. The group won't accept your mail, and group addresses rarely suit cold or marketing sends anyway.
- Will verifying my list prevent 550 5.7.124?
- Not directly; the group exists, so a mailbox check can't see the posting restriction. Flagging role and group addresses in a list is the useful step.
Clean the list before the next send.
A bounce report only tells you about the addresses you already mailed. The rest of the list has the same kinds of dead mailboxes in it, and each one becomes a hard bounce recorded against your domain the moment you send.
- A real SMTP mailbox check on every row, before anything is sent
- Dead and mistyped addresses split out, so they never reach your sending tool
- Catch-all, disposable and role addresses flagged alongside
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More Microsoft replies: every Outlook and Microsoft 365 SMTP error, and the 550 5.7.515 bulk sender rules.
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
- 550 5.5.0 — Mailbox unavailable (Outlook.com, Hotmail)
- 550 5.7.12 — Sender not authenticated by organization (Microsoft 365)
- 550 5.7.513 — Blocked by the recipient's own block list (Microsoft 365)
Sources
- Source: Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Online
- Source: RFC 3463: Enhanced Mail System Status Codes
Provider wording is quoted only where the provider publishes it.
Last reviewed 2026-10-22