My emails are all being rejected as suspected spam

Question

All the emails from my hotmail account are all being returned to me saying they were rejected as eing suspected spam by the recipient email (code 550 5.7.520) They are email addresses I have contacted many times before with no issue. I have delisted my laptop IP address with microsoft which was successful but there has been no improvement and this is also now happening on my phone linked to the email address. Can you advise what to try next please

Answer 1

Hi Centenary Theatre Company

If the AI steps do not help, please also try:  

• Rule out account compromise  
  • Review your Microsoft account sign-in activity. If you see anything unfamiliar, select “This wasn’t me” and secure the account. 
  • Then follow Microsoft’s compromised-account guidance to secure the account (change password, review security options).  
• Test a “clean” message to see if content/format is triggering the block 
  • From Outlook.com on the web, send a brand‑new email to a single recipient with: plain text, no signature, no links, no attachments. Switch to plain text format in Outlook.  
• If the clean email works, rebuild your normal message gradually 
  • Add back only one element at a time (signature, then links, then attachments) to identify what triggers the rejection.   
• Reduce reputation triggers Microsoft calls out for deliverability 
  • Avoid sending to many recipients at once, avoid heavy BCC use, and avoid sending repeatedly to recipients who don’t engage. Ask recipients to add your address to their Safe Senders list. See: Sender Support in Outlook.com - Microsoft Support 

If you still get 550 5.7.520 even with the plain‑text, no‑link, no‑attachment, single‑recipient test, reply with the single diagnostic line from the bounce, with all email addresses removed, so the block type can be identified precisely.  

Please tell me how it goes. If the problem persists, please don’t hesitate to reply to this thread and I will be happy to help. Have a lovely day!   

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Answer 2

Error code 550 5.7.520 indicates that outgoing messages are being treated as spam by recipient systems, even to contacts that previously worked. Since delisting the local IP did not help and the issue occurs from multiple devices, the problem is likely with the Outlook.com/Hotmail sending reputation or account, not the specific device IP.

Take these steps:

1. Confirm the exact NDR text
   Check one of the returned messages and confirm it is a 5.7.x “access denied/blocked/listed as spam” type error. Errors that mention being “blocked” or “listed in” a blacklist mean the recipient’s system believes the sending service or account is a spam source.
2. Use Outlook.com sender support for deliverability issues
   Since this is an Outlook.com/Hotmail consumer account and messages are being rejected as spam, use the Outlook.com sender support channel for deliverability problems:
   • Go to the Outlook.com sender support troubleshooting form referenced under “Troubleshooting tips for IT admins” and submit a deliverability issue for Outlook.com addresses.
   • Clearly state that:
     • The account is a personal Hotmail/Outlook.com mailbox.
     • All outbound mail is being rejected with 550 5.7.520 as suspected spam.
     • Delisting the IP has already been done but the issue persists across devices.
3. Check that messages are not abusive or spam-like
   Microsoft’s anti-spam systems and downstream providers will continue to block if content or patterns look abusive. Before sending again:
   • Avoid bulk sends or identical messages to many recipients.
   • Remove links or attachments that might look suspicious.
   • Ensure the account is not compromised and being used to send unsolicited mail.
4. If the IP or account is blocked at Microsoft 365 level
   If any NDRs reference being on a Microsoft 365 blocked senders list (for example 5.7.606–649 with a link to https://sender.office.com), follow these steps:
   • Go to the Office 365 Anti-Spam IP Delist Portal at https://sender.office.com.
   • Enter the email address that received the NDR and the IP address shown in the error.
   • Submit the form, then use the confirmation email to return to the portal and select Delist IP.
   • Allow up to 24 hours or more for restrictions to clear and test again.
5. If you see 5.7.511 instead
   If any NDRs show 5.7.511 Access denied, banned sender, the delist portal cannot be used. In that case:
   • Forward the full NDR (including the error and IP) to delist@microsoft.com as instructed.
   • Wait for the response (typically within 48 hours) with next steps.
6. If recipients’ servers are blocking you via third-party lists
   If the NDR mentions terms like “blocked” or “listed in” and references sites such as “spamcop,” “spamhaus,” etc., then the recipient’s server is blocking based on its own spam/blacklist filters. In that case:
   • Ask the recipient (using another email address or channel) to contact their email provider’s support and request that your Outlook.com/Hotmail address or sending service be unblocked.

If, after these steps, messages are still rejected, continue working with Outlook.com sender support and the affected recipients’ providers, as only they can adjust the spam reputation and unblock the account or service.

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References:

• Sender Support in Outlook.com
• External senders - Use the delist portal to remove yourself from the blocked senders list and address 5.7.511 Access denied errors
• Sent email in Outlook.com comes back "delivery failed"