I sent an email to a friend, but it came back undeliverable with the User or Host blacklisted?

Question

Can you tell me why this is happening? It has happened before with other friends.

Answer 1

Hello

Can you please share the comlete error message, and edit to remove your email address to protect your privacy?

Answer 2

When you receive an undeliverable email message indicating that the user or host is blacklisted, it typically means that the email server has blocked your message due to various reasons related to spam or security policies. Here are some common causes:

1. Blocked Sender IP: Your sending IP address may have been flagged for sending spam or malicious content in the past, leading to it being blacklisted.
2. Recipient's Email Provider: The recipient's email provider may have specific filters that block emails from certain senders or IP addresses deemed suspicious.
3. Spam Reports: If multiple users report your emails as spam, this can contribute to your email address or IP being blacklisted.
4. Email Content: The content of your email may trigger spam filters, especially if it contains certain keywords or attachments that are commonly associated with spam.

If you believe this is an error, you can follow the instructions in the non-delivery report (NDR) to resolve the issue, which may include requesting removal from the blacklist.

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References:

• External senders - Troubleshoot email sent to Microsoft 365
• Emails sent from Internet or application created emails are not delivered to users