sent emails from outlook 365 keep ending up in Spam

Hi @Walter Hill, 

Good day, and I appreciate the clear description of your issue.  

From your description, emails you send from Microsoft 365 Outlook are landing in recipients’ Spam or Junk folders, so you cannot confirm they received them. 

This behavior can happen when the recipient’s mail system classifies the message as spam or bulk based on filtering signals, even though the message appears in your Sent Items.  It can also occur when the sending domain is not fully authenticated, for example if SPF, DKIM, or DMARC are missing or not aligned, which reduces trust and increases the chance of spam placement.  In some cases, Microsoft 365 outbound protections may apply additional scrutiny to protect tenants, and that can influence delivery outcomes depending on sending patterns and policy. 

Below is a clear and detailed guide to walk you through the steps that can restore your user’s ability to receive emails. If you don't have a permission, please contact your IT's administrator to follow this steps below:    

1/ Run Message Trace and review Audit Logs  

• Please involve your tenant admin to run a message trace in the Exchange Admin Center (EAC). This will help determine whether the email was ever received by EOP and provide visibility into its delivery status. Run a message trace and view the results in the Exchange admin center in Exchange Online | Microsof… 
• If the trace shows no record of the email, it confirms that the message did not reach Exchange and may have been blocked or failed at the connector level. 
• Review Audit Logs in Microsoft Purview to identify any unusual activity or configuration changes.  

• For your reference: Search the audit log | Microsoft Learn  

2/ Review Mail Flow Rules and Anti-Spam Settings  

Sometimes, mail flow rules or spam filters may prevent emails from reaching the inbox.  

• Go to the Exchange Admin Center.  
• Navigate to Mail Flow > Rules and check for any rules that might redirect or block incoming emails.  
• Also review Anti-Spam Policies under Microsoft 365 Defender > Policies & Rules.  

Make sure there are no filters or rules targeting the affected user’s mailbox.  

3/  Check Accepted Domains:  

• In EAC, go to Mail flow > Accepted domains.  
• Ensure that the user's email domain is correctly listed as an "Authoritative" accepted domain. If it's not, or if there's a misconfiguration, it could prevent incoming mail.  
• Verify the SPF record includes Microsoft 365 for your domain, because SPF helps recipient systems trust your sending source.  
• Enable DKIM for the domain so messages are signed and can pass authentication checks on the recipient side.  
• Publish a DMARC policy that aligns with SPF or DKIM, then retest delivery to external recipients after DNS changes have propagated. 

4/ Check Individual Mailbox Settings:  

• Junk Email Settings (Outlook/OWA): While less likely to completely block all incoming mail, an aggressive junk mail setting or a large "Blocked Senders" list could be preventing legitimate emails. Have the user check their own blocked senders list in Outlook/OWA.  
• Mailbox Quota: Is the user's mailbox full? If so, they won't be able to receive new emails. Check their mailbox quota and usage in EAC under Recipients > Mailboxes.  

5/ Contact IT administrator:    

Since your account is managed by your organization, please contact your IT administrator to review your permissions and policies. If the issue persists after these checks, ask your IT administrator to submit a support request directly to Microsoft Support team.         

They can raise a support ticket by visiting: Get support - Microsoft 365 admin | Microsoft Learn    

As community moderators, we appreciate your understanding that our access to internal development details is limited. Our primary role is to guide users toward the appropriate resources and support channels. While we may not have visibility into deeper backend analysis, we’ll continue doing our best to support you within the scope of our responsibilities.        

I hope this information is helpful. Please follow these steps and let me know if it works for you. If you have any updates regarding the issue, please feel free to share them with me.          

Thank you for your patience and your understanding. I look forward to continuing the conversation. 

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment”.     

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When messages sent from Outlook 365 land in recipients’ Junk/Spam, the fix is on the recipient side and, for external domains, sometimes on the sending IP reputation side.

Start with what recipients can do:

1. Ask recipients to mark messages as “Not junk”
   • In Outlook/Outlook on the web, recipients should open one of the messages in their Junk Email folder and mark it as Not junk. This helps train Microsoft 365’s filters.
2. Ask recipients to add the sender to Safe senders
   • In Outlook on the web / new Outlook for Windows:
     1. At the top of the page, select Settings.
     2. Select Mail > Junk email.
     3. Under Safe senders and domains, select Add safe sender and enter the full email address or domain (for example, example.com).
     4. Select OK, then Save.
   • Messages from addresses or domains on the Safe senders list will not be moved to Junk Email.
3. Ask recipients to check their Blocked senders list
   • If the address or domain is accidentally blocked, messages will always go to Junk:
     • In Outlook.com/Outlook on the web:
       1. Sign in.
       2. Select Settings > Options or Mail.
       3. Go to Blocked senders or Block and allow.
       4. If the sender’s address or domain appears, select it and remove it.
4. If messages are going to Junk in Microsoft 365 organizations
   • The recipient’s admin can:
     • Check if the sender’s IP or domain is being filtered as spam.
     • Submit a sample as a false positive to Microsoft using the “Report message” add-in or the submission process described in Report messages and files to Microsoft.
5. If recipients get NDRs or the sending IP is blocked
   • If any recipient sees a non-delivery report (NDR) mentioning “Access denied, banned sending IP” or similar, the owner of the sending system must follow the instructions in the NDR or use the delist portal described in the Microsoft 365 mail flow troubleshooting guidance.

Because the filtering happens on the recipient side, there is no setting in Outlook on the sender’s desktop that guarantees delivery to Inbox; the reliable fixes are:

• Recipients adding the sender to Safe senders and domains.
• Ensuring the sender is not on any Blocked senders list.
• For admins, correcting any IP/domain reputation issues and submitting false positives to Microsoft.

References:

• Filter junk email and spam in Outlook
• External senders - Troubleshoot email sent to Microsoft 365
• Where are my email messages or calendar events in Mail and Calendar for Windows 10?