Microsoft (Outlook.com and Microsoft 365) · permanent error
550 5.1.20: several From addresses but no Sender
The message lists more than one address in its From header and none in its Sender header, which RFC 5322 does not allow.
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At a glance
- Code
- 550 5.1.20
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 5.1.20 Multiple From addresses are not allowed without Sender address
What it means
RFC 5322 permits a From header with several addresses only if a Sender header names the single address that actually sent the message. Exchange Online enforces that rule and rejects messages that break it with 550 5.1.20. Such messages are rare and usually come from scripts or applications that build their own headers. Many email clients do not support them anyway, so Microsoft's advice is to send with a single From address.
Common causes
- An application or script put two or more addresses in the From header.
- The message has several From addresses and no Sender header.
How to fix it
- 01Send with a single address in the From header.
- 02If several From addresses are really needed, add a Sender header containing exactly one address.
- 03Ask your admin if you cannot change how the sending application builds its headers.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- NDR error code 550 5.1.20 "Multiple From addresses are not allowed without Sender address"learn.microsoft.com
- Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
Related codes
Further reading
All 111 Microsoft codesEvery code in the wikiPaste your own bounce