# 550 5.7.703: messages blocked by your organization using Tenant Allow Block List URL: https://iblockspam.com/smtp-errors/550-5-7-703 Last updated: 2026-10-22 Code: 550 5.7.703 (permanent failure, the message bounced) Provider: Microsoft 365 / Outlook.com 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 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. 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. ## Common 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 (sender) - Check the recipients named in the NDR and resend without the blocked ones if they aren't needed. - Ask your admin whether the block is intentional. Only an admin can change the list. - 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. ## How to fix it (recipient or admin) - External recipients can't change the sender's list; the sender's admin controls the block. **Q: 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. **Q: 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: - Fix NDR error codes 550 5.7.703, 550 5.7.705, 550 5.7.708, and 550 5.7.750 (Microsoft Learn): https://learn.microsoft.com/en-us/troubleshoot/exchange/email-delivery/ndr/fix-error-codes-550-5-7-703-550-5-7-705-550-5-7-708-550-5-7-750 - Allow or block email using the Tenant Allow/Block List (Microsoft Learn): https://learn.microsoft.com/en-us/defender-office-365/tenant-allow-block-list-email-spoof-configure - Email nondelivery reports (NDRs) and SMTP errors in Exchange Online (Microsoft Learn): https://learn.microsoft.com/en-us/troubleshoot/exchange/email-delivery/ndr/non-delivery-reports-in-exchange-online --- Source: iBlockSpam, https://iblockspam.com/smtp-errors/550-5-7-703 (this is a Markdown copy; the HTML page is canonical). Quote with attribution and a link. Site index for AI assistants: https://iblockspam.com/llms.txt