Enhanced SMTP status code · RFC 3463 · IANA
5.7.124 Sender not in allowed-senders list
The sender is not on the list of those allowed to send to this distribution group.
- Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1).
- Subject: X.7 · Security and policy
Policies (per-host or per-recipient filters) and cryptographic operations; up to the sender, the recipient or both.
How 5.7.124 appears at providers
The exact text from the provider's documentation, as you see it in the bounce, and what it means.
Microsoft 365 / Exchange Online
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5.7.124
Sender not in allowed-senders list
The sender is not on the list of those allowed to send to this distribution group.
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026