Enhanced SMTP status code · RFC 3463 · IANA
5.7.520 Access denied, Your organization does not allow external forwarding
The sender's organisation does not allow automatic forwarding outside it.
- 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 5.7.520 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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5.7.520
Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)
The sender's organisation does not allow automatic forwarding outside it.
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026