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SMTP error code · Microsoft 365 / Outlook.com

550 5.7.703: messages blocked by your organization using Tenant Allow Block List

550 5.7.703 Permanent failure (5xx): the message bounced
By iBlockSpam Team Checked against sources 3 sources How we check our content
What it means

Someone in your organization emailed an address or domain that your Microsoft 365 admins blocked in the Tenant Allow/Block List, so the whole message was stopped.

What the bounce says
Your message can't be delivered because messages to <recipients> are blocked by your organization using Tenant Allow Block List.

The complete NDR text as given in Microsoft's article on 5.7.703, 5.7.705, 5.7.708 and 5.7.750.

What 550 5.7.703 means

Microsoft documents 550 5.7.703 as the NDR a user gets when sending to an email address or domain that's blocked in the Tenant Allow/Block List. That list holds external senders blocked from emailing your users, and Microsoft says it works in both directions: users in the organization also can't send email to blocked domains and addresses.

The block applies to the whole message. If even one recipient address or domain in a message matches a block entry, Microsoft says the message is blocked for all other internal and external recipients too. So one blocked address on a long Cc line can stop the message for everyone.

Only an email admin can change the Tenant Allow/Block List. Admins find block entries in the Microsoft Defender portal under Tenant Allow/Block Lists, on the Domains & addresses tab. Before removing an entry, check why it was added: entries can also be created when someone submits a message as a threat and chooses to block the sender or domain. Block entries can be set to expire, with 30 days as the default. Also note how domain entries match: Microsoft says an entry for contoso.com doesn't block subdomains, and *.contoso.com doesn't block contoso.com itself.

Likely causes

  • The recipient's address or domain has a block entry in the Tenant Allow/Block List.
  • A block entry was added when a message from that sender or domain was submitted to Microsoft as a threat.
  • One blocked recipient on the message, which blocks delivery to every recipient.

How to fix it

If you sent the message

  1. Check the recipients named in the NDR and resend without the blocked ones if they aren't needed.
  2. Ask your admin whether the block is intentional. Only an admin can change the list.
  3. Admins: review the entry under Tenant Allow/Block Lists, Domains & addresses tab, in the Microsoft Defender portal, and remove or let it expire if it's no longer needed.

If you're the recipient or their admin

  1. External recipients can't change the sender's list; the sender's admin controls the block.
Email Health Check Email Header Analyzer

Frequently asked questions

Why did 5.7.703 stop the message for every recipient, not just one?

Microsoft says that if one recipient address or domain in a message is blocked in the Tenant Allow/Block List, the entire message is blocked for all internal and external recipients. Remove the blocked recipient and resend.

Does blocking a domain in Microsoft 365 also stop outgoing mail to it?

Yes. Microsoft says users in the organization can't send email to domains and addresses blocked in the Tenant Allow/Block List; they get the 550 5.7.703 NDR instead.

Sources

  1. Fix NDR error codes 550 5.7.703, 550 5.7.705, 550 5.7.708, and 550 5.7.750 (Microsoft Learn)
  2. Allow or block email using the Tenant Allow/Block List (Microsoft Learn)
  3. Email nondelivery reports (NDRs) and SMTP errors in Exchange Online (Microsoft Learn)

Provider messages are quoted as the provider publishes them. Servers can change their wording, so the bounce you received may differ slightly.

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