Outlook using 365 rejecting emails with attachment

It sounds like you are experiencing issues with receiving emails that contain attachments, and this could be related to email filtering or security settings within Microsoft 365. Here are some potential reasons and solutions:

1. Email Filtering: Microsoft 365 has built-in security features that may reject emails with attachments if they are flagged as suspicious. Ensure that the senders are added to your safe senders list, but also verify that their email practices comply with Microsoft’s standards.
2. Domain Reputation: If the sending domain (like Stifel.com) has a poor reputation or if their email practices are not compliant with standards (like SPF, DKIM, and DMARC), emails from them might be rejected. You may want to check with your broker to ensure their email configuration is correct.
3. Attachment Size and Type: Check if there are any size limits or restrictions on the types of attachments that can be received. Microsoft 365 has specific limits for attachment sizes.
4. Network Issues: Sometimes, network configurations or firewalls can interfere with email delivery. Ensure that your network allows connections from Microsoft 365 datacenters.
5. Support and Recovery Assistant: You can use the Microsoft Support and Recovery Assistant to diagnose and fix issues with sending and receiving emails in Outlook.

If the problem persists, consider reaching out to Microsoft support for further assistance, as they can provide more detailed insights into your specific situation.

References:

• Help Identify My Issue with Sending/Receiving Email in Outlook (Automatic Checks)
• External senders - Troubleshoot email sent to Microsoft 365

Hi Joe,

Thanks for reaching out about the issue you're experiencing with Outlook rejecting emails that contain attachments. I understand how frustrating it must be especially when these emails are coming from trusted contacts like your broker and other companies you've communicated with regularly.

It sounds like you're dealing with a situation where Microsoft 365 is flagging incoming emails with attachments as suspicious, even though they’re from safe sources. This can happen due to recent updates in spam filtering and security protocols especially if the attachments are PDFs or if the emails are formatted in HTML which are often scrutinized more heavily due to phishing risks.

To help resolve this I recommend trying a different approach than the initial solution. Instead of relying solely on safe sender settings, ask your contacts to send attachments using a shared link from OneDrive or another secure cloud service. This method is less likely to be flagged by Microsoft 365’s filters and ensures the content reaches you safely. Additionally you can check your Outlook settings and switch your message format to plain text, which has helped other users bypass these filters when receiving attachments.

Would you be able to confirm whether the attachments being rejected are mostly PDFs or if the emails are formatted in HTML?

I hope this answer is helpful if you have further questions feel free to reply back

Regards,

Marcelo